diff --git a/include/m_ctype.h b/include/m_ctype.h
index 6812445c6d54b..0a8250538687a 100644
--- a/include/m_ctype.h
+++ b/include/m_ctype.h
@@ -287,6 +287,7 @@ extern MY_UNI_CTYPE my_uni_ctype[256];
 #define MY_CS_NON1TO1 0x40000  /* Has a complex mapping from characters
                                   to weights, e.g. contractions, expansions,
                                   ignorable characters */
+#define MY_CS_UPPER_EQUAL_AS_EQUAL 0x80000 /* (UPPER(x)=UPPER(y)) <=> (x=y)*/
 #define MY_CHARSET_UNDEFINED 0
 
 /* Character repertoire flags */
diff --git a/libmysqld/CMakeLists.txt b/libmysqld/CMakeLists.txt
index 10f505b40a14e..2042f7fe321e8 100644
--- a/libmysqld/CMakeLists.txt
+++ b/libmysqld/CMakeLists.txt
@@ -71,6 +71,7 @@ SET(SQL_EMBEDDED_SOURCES emb_qcache.cc libmysqld.c lib_sql.cc
            ../sql/mf_iocache.cc ../sql/my_decimal.cc 
            ../sql/net_serv.cc ../sql/opt_range.cc
            ../sql/opt_rewrite_date_cmp.cc
+           ../sql/opt_rewrite_remove_casefold.cc
            ../sql/opt_sum.cc
            ../sql/parse_file.cc ../sql/procedure.cc ../sql/protocol.cc 
            ../sql/records.cc ../sql/repl_failsafe.cc ../sql/rpl_filter.cc
diff --git a/mysql-test/include/sargable_casefold.inc b/mysql-test/include/sargable_casefold.inc
new file mode 100644
index 0000000000000..c10e78e62c810
--- /dev/null
+++ b/mysql-test/include/sargable_casefold.inc
@@ -0,0 +1,44 @@
+# Check sargable_casefold rewrite for $collation
+
+eval create table t1 (
+  col1 varchar(32), 
+  col2 varchar(32), 
+  col3 char(32), 
+  col4  text, 
+  key(col1),
+  key(col2),
+  key(col3),
+  key(col4(32))
+) collate $collation;
+
+insert into t1
+select 
+  concat('A-', seq),
+  concat('A-', seq),
+  concat('A-', seq),
+  concat('A-', seq)
+from seq_1_to_100;
+
+analyze table t1 persistent for all;
+
+--echo # Basic examples. All should use ref(col1):
+explain
+select * from t1 where upper(col1)='A-3';
+select * from t1 where upper(col1)='A-3';
+
+explain
+select * from t1 where ucase(col1)='a-3';
+select * from t1 where ucase(col1)='a-3';
+
+explain select * from t1 where 'abc'=upper(col1);
+explain select * from t1 where 'xyz'=ucase(col1);
+
+create view v1 as select * from t1;
+explain select * from v1 where 'abc'=upper(col1);
+drop view v1;
+
+explain select * from t1 where upper(col3)='a-3';
+explain select * from t1 where upper(col4)='a-3';
+
+# DROP TABLE t1 is missing intentionally here.
+
diff --git a/mysql-test/main/mysqld--help.result b/mysql-test/main/mysqld--help.result
index 33b7698226b8a..3c5d7c591344c 100644
--- a/mysql-test/main/mysqld--help.result
+++ b/mysql-test/main/mysqld--help.result
@@ -804,7 +804,7 @@ The following specify which files/extra groups are read (specified before remain
  condition_pushdown_for_derived, split_materialized, 
  condition_pushdown_for_subquery, rowid_filter, 
  condition_pushdown_from_having, not_null_range_scan, 
- hash_join_cardinality
+ hash_join_cardinality, sargable_casefold
  --optimizer-trace=name 
  Controls tracing of the Optimizer:
  optimizer_trace=option=val[,option=val...], where option
@@ -1764,7 +1764,7 @@ optimizer-rowid-copy-cost 0.002653
 optimizer-scan-setup-cost 10
 optimizer-search-depth 62
 optimizer-selectivity-sampling-limit 100
-optimizer-switch index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+optimizer-switch index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 optimizer-trace 
 optimizer-trace-max-mem-size 1048576
 optimizer-use-condition-selectivity 4
diff --git a/mysql-test/main/mysqltest_tracking_info.result b/mysql-test/main/mysqltest_tracking_info.result
index c4fedd6b59c8c..93441ff12bf56 100644
--- a/mysql-test/main/mysqltest_tracking_info.result
+++ b/mysql-test/main/mysqltest_tracking_info.result
@@ -38,7 +38,7 @@ SET @@session.session_track_system_variables='optimizer_switch';
 set optimizer_switch='index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off';
 -- Tracker : SESSION_TRACK_SYSTEM_VARIABLES
 -- optimizer_switch
--- index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+-- index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=on,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 
 Warnings:
 Warning	1681	'engine_condition_pushdown=on' is deprecated and will be removed in a future release
diff --git a/mysql-test/main/sargable_casefold.result b/mysql-test/main/sargable_casefold.result
new file mode 100644
index 0000000000000..d9488b983e22c
--- /dev/null
+++ b/mysql-test/main/sargable_casefold.result
@@ -0,0 +1,278 @@
+set
+@tmp_switch_sarg_casefold=@@optimizer_switch,
+optimizer_switch='sargable_casefold=on';
+create table t1 (
+col1 varchar(32), 
+col2 varchar(32), 
+col3 char(32), 
+col4  text, 
+key(col1),
+key(col2),
+key(col3),
+key(col4(32))
+) collate utf8mb3_general_ci;
+insert into t1
+select 
+concat('A-', seq),
+concat('A-', seq),
+concat('A-', seq),
+concat('A-', seq)
+from seq_1_to_100;
+analyze table t1 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 'col4'
+test.t1	analyze	status	Table is already up to date
+# Basic examples. All should use ref(col1):
+explain
+select * from t1 where upper(col1)='A-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+select * from t1 where upper(col1)='A-3';
+col1	col2	col3	col4
+A-3	A-3	A-3	A-3
+explain
+select * from t1 where ucase(col1)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+select * from t1 where ucase(col1)='a-3';
+col1	col2	col3	col4
+A-3	A-3	A-3	A-3
+explain select * from t1 where 'abc'=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+explain select * from t1 where 'xyz'=ucase(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+create view v1 as select * from t1;
+explain select * from v1 where 'abc'=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+drop view v1;
+explain select * from t1 where upper(col3)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col3	col3	97	const	1	Using index condition
+explain select * from t1 where upper(col4)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col4	col4	99	const	1	Using where
+# must not be rewritten:
+explain select * from t1 where ucase(col1 collate utf8mb3_bin)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+# Will not do the rewrite due to collation mismatch:
+explain select * from t1 where ucase(col1)=_utf8mb3'abc' COLLATE utf8mb3_bin;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+drop table t1;
+create table t1 (
+col1 varchar(32), 
+col2 varchar(32), 
+col3 char(32), 
+col4  text, 
+key(col1),
+key(col2),
+key(col3),
+key(col4(32))
+) collate utf8mb4_general_ci;
+insert into t1
+select 
+concat('A-', seq),
+concat('A-', seq),
+concat('A-', seq),
+concat('A-', seq)
+from seq_1_to_100;
+analyze table t1 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 'col4'
+test.t1	analyze	status	Table is already up to date
+# Basic examples. All should use ref(col1):
+explain
+select * from t1 where upper(col1)='A-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	131	const	1	Using index condition
+select * from t1 where upper(col1)='A-3';
+col1	col2	col3	col4
+A-3	A-3	A-3	A-3
+explain
+select * from t1 where ucase(col1)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	131	const	1	Using index condition
+select * from t1 where ucase(col1)='a-3';
+col1	col2	col3	col4
+A-3	A-3	A-3	A-3
+explain select * from t1 where 'abc'=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	131	const	1	Using index condition
+explain select * from t1 where 'xyz'=ucase(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	131	const	1	Using index condition
+create view v1 as select * from t1;
+explain select * from v1 where 'abc'=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	131	const	1	Using index condition
+drop view v1;
+explain select * from t1 where upper(col3)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col3	col3	129	const	1	Using index condition
+explain select * from t1 where upper(col4)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col4	col4	131	const	1	Using where
+# must not be rewritten:
+explain select * from t1 where ucase(col1 collate utf8mb4_bin)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+# Will not do the rewrite due to collation mismatch:
+explain select * from t1 where ucase(col1)=_utf8mb4'abc' COLLATE utf8mb4_bin;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+#
+# Check if optimizer_switch turns the rewrite off:
+#
+set 
+@save_os=@@optimizer_switch, 
+optimizer_switch='sargable_casefold=off';
+explain select * from t1 where upper(col1)='A-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+explain select * from t1 where ucase(col1)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+set optimizer_switch=@save_os;
+# The following will not do the rewrite because the comparison
+# is done as DOUBLEs. Come to think of it, it won't harm to do
+# the rewrite but it is outside of the scope of this patch:
+explain select * from t1 where ucase(col1)=123.456;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+select
+coercibility(upper(col1))
+from t1 limit 1;
+coercibility(upper(col1))
+2
+select coercibility(_utf8mb3'abc' COLLATE utf8mb3_bin);
+coercibility(_utf8mb3'abc' COLLATE utf8mb3_bin)
+0
+# This is transformed too even if it doesn't create any new
+# [potential] access paths:
+explain format=json select * from t1 where upper(col1)=upper(col2);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "cost": 0.0256761,
+    "nested_loop": [
+      {
+        "table": {
+          "table_name": "t1",
+          "access_type": "ALL",
+          "loops": 1,
+          "rows": 100,
+          "cost": 0.0256761,
+          "filtered": 100,
+          "attached_condition": "t1.col2 = t1.col1"
+        }
+      }
+    ]
+  }
+}
+#
+# Check if ref access works
+#
+create table t2 (
+a varchar(32),
+non_key varchar(32),
+key(a)
+) collate utf8mb4_general_ci;
+insert into t2
+select
+concat('A-', seq),
+concat('A-', seq)
+from seq_1_to_10;
+# Must use ref access for t1:
+explain select * from t1, t2 where upper(t1.col1)= t2.non_key;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t1	ref	col1	col1	131	test.t2.non_key	1	
+create table t3 (
+a varchar(32),
+b varchar(32),
+key(a),
+key(b)
+) collate utf8mb3_general_ci;
+insert into t3 values ('abc','ABC'), ('xyz','XYZ');
+explain extended
+select a from t3 ignore index(a) where a=b and upper(b)='ABC';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t3	ref	b	b	99	const	1	100.00	Using index condition; Using where
+Warnings:
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` IGNORE INDEX (`a`) where `test`.`t3`.`a` = `test`.`t3`.`b` and `test`.`t3`.`b` = 'ABC'
+#
+# Check that rewrite isn't applied for non-applicable collations
+#
+create table t4 (
+col1 varchar(32) collate utf8mb3_bin,
+col2 varchar(32) collate utf8mb3_czech_ci,
+col3 varchar(32) collate latin1_bin,
+key(col1),
+key(col2),
+key(col3)
+);
+insert into t4
+select 
+concat('A-', seq),
+concat('A-', seq),
+concat('A-', seq)
+from seq_1_to_100;
+analyze table t4 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t4	analyze	status	Engine-independent statistics collected
+test.t4	analyze	status	Table is already up to date
+# None should use ref access:
+explain select * from t4 where upper(col1)='A-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t4	ALL	NULL	NULL	NULL	NULL	100	Using where
+explain select * from t4 where upper(col2)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t4	ALL	NULL	NULL	NULL	NULL	100	Using where
+explain select * from t4 where upper(col3)='a-3';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t4	ALL	NULL	NULL	NULL	NULL	100	Using where
+#
+# Check that rewrite works for UPPER(col) IN (const-list)
+#
+set
+@tmp_ot= @@optimizer_trace,
+optimizer_trace=1;
+# must use range:
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	131	NULL	3	Using index condition
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+col1	col2	col3	col4
+A-3	A-3	A-3	A-3
+A-4	A-4	A-4	A-4
+A-5	A-5	A-5	A-5
+# Will not use the rewrite:
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4',col2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+#
+# MDEV-31946: Optimizer handle UCASE(varchar_col)=... does not work for UPDATE/DELETE
+#
+explain delete from t1 where upper(col1)='A';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	131	NULL	1	Using where
+explain delete from t1 where upper(col1) IN ('A','B');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	131	NULL	2	Using where
+explain update t1 set col2='ABC' where upper(col1)='A';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	131	NULL	1	Using where
+explain update t1 set col2='ABC' where upper(col1) IN ('A','B');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	131	NULL	2	Using where
+drop table t1,t2,t3,t4;
+set optimizer_switch=@tmp_switch_sarg_casefold;
diff --git a/mysql-test/main/sargable_casefold.test b/mysql-test/main/sargable_casefold.test
new file mode 100644
index 0000000000000..abb95d2b07949
--- /dev/null
+++ b/mysql-test/main/sargable_casefold.test
@@ -0,0 +1,141 @@
+#
+# MDEV-31496 Make optimizer handle UCASE(varchar_col)=...
+#
+--source include/have_sequence.inc
+
+set
+  @tmp_switch_sarg_casefold=@@optimizer_switch,
+  optimizer_switch='sargable_casefold=on';
+
+let $collation=utf8mb3_general_ci;
+source include/sargable_casefold.inc;
+
+--echo # must not be rewritten:
+explain select * from t1 where ucase(col1 collate utf8mb3_bin)='a-3';
+
+--echo # Will not do the rewrite due to collation mismatch:
+explain select * from t1 where ucase(col1)=_utf8mb3'abc' COLLATE utf8mb3_bin;
+drop table t1;
+
+let $collation=utf8mb4_general_ci;
+source include/sargable_casefold.inc;
+
+--echo # must not be rewritten:
+explain select * from t1 where ucase(col1 collate utf8mb4_bin)='a-3';
+
+--echo # Will not do the rewrite due to collation mismatch:
+explain select * from t1 where ucase(col1)=_utf8mb4'abc' COLLATE utf8mb4_bin;
+
+--echo #
+--echo # Check if optimizer_switch turns the rewrite off:
+--echo #
+
+set 
+  @save_os=@@optimizer_switch, 
+  optimizer_switch='sargable_casefold=off';
+explain select * from t1 where upper(col1)='A-3';
+explain select * from t1 where ucase(col1)='a-3';
+
+set optimizer_switch=@save_os;
+
+--echo # The following will not do the rewrite because the comparison
+--echo # is done as DOUBLEs. Come to think of it, it won't harm to do
+--echo # the rewrite but it is outside of the scope of this patch:
+explain select * from t1 where ucase(col1)=123.456;
+
+select
+  coercibility(upper(col1))
+from t1 limit 1;
+select coercibility(_utf8mb3'abc' COLLATE utf8mb3_bin);
+
+
+--echo # This is transformed too even if it doesn't create any new
+--echo # [potential] access paths:
+explain format=json select * from t1 where upper(col1)=upper(col2);
+
+
+--echo #
+--echo # Check if ref access works
+--echo #
+create table t2 (
+  a varchar(32),
+  non_key varchar(32),
+  key(a)
+) collate utf8mb4_general_ci;
+
+insert into t2
+select
+  concat('A-', seq),
+  concat('A-', seq)
+from seq_1_to_10;
+
+--echo # Must use ref access for t1:
+explain select * from t1, t2 where upper(t1.col1)= t2.non_key;
+
+# Check the interplay with equality propagation
+
+create table t3 (
+  a varchar(32),
+  b varchar(32),
+  key(a),
+  key(b)
+) collate utf8mb3_general_ci;
+insert into t3 values ('abc','ABC'), ('xyz','XYZ');
+
+explain extended
+select a from t3 ignore index(a) where a=b and upper(b)='ABC';
+
+--echo #
+--echo # Check that rewrite isn't applied for non-applicable collations
+--echo #
+create table t4 (
+  col1 varchar(32) collate utf8mb3_bin,
+  col2 varchar(32) collate utf8mb3_czech_ci,
+  col3 varchar(32) collate latin1_bin,
+  key(col1),
+  key(col2),
+  key(col3)
+);
+
+insert into t4
+select 
+  concat('A-', seq),
+  concat('A-', seq),
+  concat('A-', seq)
+from seq_1_to_100;
+
+analyze table t4 persistent for all;
+
+--echo # None should use ref access:
+explain select * from t4 where upper(col1)='A-3';
+explain select * from t4 where upper(col2)='a-3';
+explain select * from t4 where upper(col3)='a-3';
+
+--echo #
+--echo # Check that rewrite works for UPPER(col) IN (const-list)
+--echo #
+set
+  @tmp_ot= @@optimizer_trace,
+  optimizer_trace=1;
+
+--echo # must use range:
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+
+--echo # Will not use the rewrite:
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4',col2);
+
+--echo #
+--echo # MDEV-31946: Optimizer handle UCASE(varchar_col)=... does not work for UPDATE/DELETE
+--echo #
+explain delete from t1 where upper(col1)='A';
+explain delete from t1 where upper(col1) IN ('A','B');
+
+explain update t1 set col2='ABC' where upper(col1)='A';
+explain update t1 set col2='ABC' where upper(col1) IN ('A','B');
+
+drop table t1,t2,t3,t4;
+
+set optimizer_switch=@tmp_switch_sarg_casefold;
diff --git a/mysql-test/main/sargable_casefold_notembedded.result b/mysql-test/main/sargable_casefold_notembedded.result
new file mode 100644
index 0000000000000..1f6e9a32754bd
--- /dev/null
+++ b/mysql-test/main/sargable_casefold_notembedded.result
@@ -0,0 +1,61 @@
+create table t1 (
+col1 varchar(32), 
+col2 varchar(32), 
+key(col1),
+key(col2)
+) collate utf8mb3_general_ci;
+insert into t1
+select 
+concat('A-', seq),
+concat('A-', seq)
+from seq_1_to_100;
+set
+@tmp_ot= @@optimizer_trace,
+@tmp_os=@@optimizer_switch,
+optimizer_switch='sargable_casefold=on',
+optimizer_trace=1;
+explain select * from t1 where 'abc'=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
+select 
+json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+JS
+[
+    {
+        "before": "'abc' = ucase(t1.col1)",
+        "after": "'abc' = t1.col1"
+    }
+]
+explain select * from t1 where ucase(col2)=upper(col1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
+select 
+json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+JS
+[
+    {
+        "before": "ucase(t1.col2) = ucase(t1.col1)",
+        "after": "t1.col2 = t1.col1"
+    }
+]
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	col1	col1	99	NULL	3	Using index condition
+# Will show the rewrite:
+select 
+json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+JS
+[
+    {
+        "before": "ucase(t1.col1) in ('A-3','A-4','a-5')",
+        "after": "t1.col1 in ('A-3','A-4','a-5')"
+    }
+]
+set 
+optimizer_trace=@tmp_ot,
+optimizer_switch=@tmp_os;
+drop table t1;
diff --git a/mysql-test/main/sargable_casefold_notembedded.test b/mysql-test/main/sargable_casefold_notembedded.test
new file mode 100644
index 0000000000000..b04e25f1cac22
--- /dev/null
+++ b/mysql-test/main/sargable_casefold_notembedded.test
@@ -0,0 +1,51 @@
+#
+# MDEV-31496 Make optimizer handle UCASE(varchar_col)=...
+#  Check the coverage in optimizer trace.
+#
+
+--source include/not_embedded.inc
+--source include/have_sequence.inc
+
+
+create table t1 (
+  col1 varchar(32), 
+  col2 varchar(32), 
+  key(col1),
+  key(col2)
+) collate utf8mb3_general_ci;
+
+insert into t1
+select 
+  concat('A-', seq),
+  concat('A-', seq)
+from seq_1_to_100;
+
+set
+  @tmp_ot= @@optimizer_trace,
+  @tmp_os=@@optimizer_switch,
+  optimizer_switch='sargable_casefold=on',
+  optimizer_trace=1;
+
+explain select * from t1 where 'abc'=upper(col1);
+select 
+  json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+
+explain select * from t1 where ucase(col2)=upper(col1);
+select 
+  json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+
+explain
+select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
+--echo # Will show the rewrite:
+select 
+  json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
+from information_schema.optimizer_trace;
+
+set 
+  optimizer_trace=@tmp_ot,
+  optimizer_switch=@tmp_os;
+
+drop table t1;
+
diff --git a/mysql-test/main/sargable_casefold_part.result b/mysql-test/main/sargable_casefold_part.result
new file mode 100644
index 0000000000000..7311be1c8dcc9
--- /dev/null
+++ b/mysql-test/main/sargable_casefold_part.result
@@ -0,0 +1,58 @@
+set
+@tmp_switch_sarg_casefold=@@optimizer_switch,
+optimizer_switch='sargable_casefold=on';
+create table t1 (
+s1 varchar(15) collate utf8mb3_bin,
+s2 varchar(15) collate utf8mb3_general_ci
+) partition by key (s2) partitions 4;
+insert into t1 values ('aa','aa'),('bb','bb');
+explain format=json select * from t1 where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "nested_loop": [
+      {
+        "table": {
+          "table_name": "t1",
+          "partitions": ["p2"],
+          "access_type": "system",
+          "rows": 1,
+          "filtered": 100
+        }
+      }
+    ]
+  }
+}
+explain format=json delete from t1 where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "delete": 1,
+      "table_name": "t1",
+      "partitions": ["p2"],
+      "access_type": "ALL",
+      "rows": 1,
+      "attached_condition": "t1.s2 = 'AA'"
+    }
+  }
+}
+explain format=json update t1 set s1='aaa' where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "update": 1,
+      "table_name": "t1",
+      "partitions": ["p2"],
+      "access_type": "ALL",
+      "rows": 1,
+      "attached_condition": "t1.s2 = 'AA'"
+    }
+  }
+}
+drop table t1;
+set optimizer_switch=@tmp_switch_sarg_casefold;
diff --git a/mysql-test/main/sargable_casefold_part.test b/mysql-test/main/sargable_casefold_part.test
new file mode 100644
index 0000000000000..0c6db1d092af2
--- /dev/null
+++ b/mysql-test/main/sargable_casefold_part.test
@@ -0,0 +1,22 @@
+--source include/have_partition.inc
+#
+# MDEV-31975: UCASE(varchar_col)=... not handled for partition tables
+#
+
+set
+  @tmp_switch_sarg_casefold=@@optimizer_switch,
+  optimizer_switch='sargable_casefold=on';
+
+create table t1 (
+  s1 varchar(15) collate utf8mb3_bin,
+  s2 varchar(15) collate utf8mb3_general_ci
+) partition by key (s2) partitions 4;
+insert into t1 values ('aa','aa'),('bb','bb');
+
+explain format=json select * from t1 where upper(s2)='AA';
+explain format=json delete from t1 where upper(s2)='AA';
+explain format=json update t1 set s1='aaa' where upper(s2)='AA';
+
+drop table t1;
+
+set optimizer_switch=@tmp_switch_sarg_casefold;
diff --git a/mysql-test/suite/sys_vars/r/optimizer_switch_basic.result b/mysql-test/suite/sys_vars/r/optimizer_switch_basic.result
index 66399f615358e..5593fc2ed50fb 100644
--- a/mysql-test/suite/sys_vars/r/optimizer_switch_basic.result
+++ b/mysql-test/suite/sys_vars/r/optimizer_switch_basic.result
@@ -1,60 +1,60 @@
 set @@global.optimizer_switch=@@optimizer_switch;
 select @@global.optimizer_switch;
 @@global.optimizer_switch
-index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 select @@session.optimizer_switch;
 @@session.optimizer_switch
-index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 show global variables like 'optimizer_switch';
 Variable_name	Value
-optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 show session variables like 'optimizer_switch';
 Variable_name	Value
-optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 select * from information_schema.global_variables where variable_name='optimizer_switch';
 VARIABLE_NAME	VARIABLE_VALUE
-OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 select * from information_schema.session_variables where variable_name='optimizer_switch';
 VARIABLE_NAME	VARIABLE_VALUE
-OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on
+OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=off,hash_join_cardinality=on,sargable_casefold=on
 set global optimizer_switch=4101;
 set session optimizer_switch=2058;
 select @@global.optimizer_switch;
 @@global.optimizer_switch
-index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 select @@session.optimizer_switch;
 @@session.optimizer_switch
-index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 set global optimizer_switch="index_merge_sort_union=on";
 set session optimizer_switch="index_merge=off";
 select @@global.optimizer_switch;
 @@global.optimizer_switch
-index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 select @@session.optimizer_switch;
 @@session.optimizer_switch
-index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 show global variables like 'optimizer_switch';
 Variable_name	Value
-optimizer_switch	index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+optimizer_switch	index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 show session variables like 'optimizer_switch';
 Variable_name	Value
-optimizer_switch	index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+optimizer_switch	index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 select * from information_schema.global_variables where variable_name='optimizer_switch';
 VARIABLE_NAME	VARIABLE_VALUE
-OPTIMIZER_SWITCH	index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+OPTIMIZER_SWITCH	index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 select * from information_schema.session_variables where variable_name='optimizer_switch';
 VARIABLE_NAME	VARIABLE_VALUE
-OPTIMIZER_SWITCH	index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+OPTIMIZER_SWITCH	index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=on,in_to_exists=off,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 set session optimizer_switch="default";
 select @@session.optimizer_switch;
 @@session.optimizer_switch
-index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off
+index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=off,partial_match_rowid_merge=off,partial_match_table_scan=off,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=off,join_cache_hashed=off,join_cache_bka=off,optimize_join_buffer_size=off,table_elimination=off,extended_keys=off,exists_to_in=off,orderby_uses_equalities=off,condition_pushdown_for_derived=off,split_materialized=off,condition_pushdown_for_subquery=off,rowid_filter=off,condition_pushdown_from_having=off,not_null_range_scan=off,hash_join_cardinality=off,sargable_casefold=off
 set optimizer_switch = replace(@@optimizer_switch, '=off', '=on');
 Warnings:
 Warning	1681	'engine_condition_pushdown=on' is deprecated and will be removed in a future release
 select @@optimizer_switch;
 @@optimizer_switch
-index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=on,hash_join_cardinality=on
+index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=on,mrr_cost_based=on,mrr_sort_keys=on,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on,not_null_range_scan=on,hash_join_cardinality=on,sargable_casefold=on
 set global optimizer_switch=1.1;
 ERROR 42000: Incorrect argument type to variable 'optimizer_switch'
 set global optimizer_switch=1e1;
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
index 0225f6709e249..e008e19e2dcfe 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
@@ -2499,7 +2499,7 @@ VARIABLE_COMMENT	Fine-tune the optimizer behavior
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL
-ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,default
+ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,sargable_casefold,default
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	OPTIMIZER_TRACE
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
index 727a7daa43144..a8e5ffec7d012 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
@@ -2699,7 +2699,7 @@ VARIABLE_COMMENT	Fine-tune the optimizer behavior
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL
-ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,default
+ENUM_VALUE_LIST	index_merge,index_merge_union,index_merge_sort_union,index_merge_intersection,index_merge_sort_intersection,engine_condition_pushdown,index_condition_pushdown,derived_merge,derived_with_keys,firstmatch,loosescan,materialization,in_to_exists,semijoin,partial_match_rowid_merge,partial_match_table_scan,subquery_cache,mrr,mrr_cost_based,mrr_sort_keys,outer_join_with_cache,semijoin_with_cache,join_cache_incremental,join_cache_hashed,join_cache_bka,optimize_join_buffer_size,table_elimination,extended_keys,exists_to_in,orderby_uses_equalities,condition_pushdown_for_derived,split_materialized,condition_pushdown_for_subquery,rowid_filter,condition_pushdown_from_having,not_null_range_scan,hash_join_cardinality,sargable_casefold,default
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	OPTIMIZER_TRACE
diff --git a/mysql-test/suite/sysschema/r/optimizer_switch.result b/mysql-test/suite/sysschema/r/optimizer_switch.result
index 4193bf0739e3e..69aadfebf104b 100644
--- a/mysql-test/suite/sysschema/r/optimizer_switch.result
+++ b/mysql-test/suite/sysschema/r/optimizer_switch.result
@@ -26,6 +26,7 @@ outer_join_with_cache	on
 partial_match_rowid_merge	on
 partial_match_table_scan	on
 rowid_filter	on
+sargable_casefold	on
 semijoin	on
 semijoin_with_cache	on
 split_materialized	on
diff --git a/sql/CMakeLists.txt b/sql/CMakeLists.txt
index 30a7088512859..16401ea1d902e 100644
--- a/sql/CMakeLists.txt
+++ b/sql/CMakeLists.txt
@@ -113,6 +113,7 @@ SET (SQL_SOURCE
                ../sql-common/client_plugin.c
                opt_range.cc
                opt_rewrite_date_cmp.cc
+               opt_rewrite_remove_casefold.cc
                opt_sum.cc
                ../sql-common/pack.c parse_file.cc password.c procedure.cc
                protocol.cc records.cc repl_failsafe.cc rpl_filter.cc
diff --git a/sql/item.h b/sql/item.h
index 468b01c5469eb..ffbe7d2064f40 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -2514,6 +2514,8 @@ class Item :public Value_source,
   { return this; }
   virtual Item *multiple_equality_transformer(THD *thd, uchar *arg)
   { return this; }
+  virtual Item* varchar_upper_cmp_transformer(THD *thd, uchar *arg)
+  { return this; }
   virtual Item* date_conds_transformer(THD *thd, uchar *arg)
   { return this; }
   virtual bool expr_cache_is_needed(THD *) { return FALSE; }
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 556374eff6a1a..91f66d55527eb 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -790,6 +790,7 @@ class Item_func_eq :public Item_bool_rowready_func2
   { return get_item_copy<Item_func_eq>(thd, this); }
   Item* date_conds_transformer(THD *thd, uchar *arg) override
   { return do_date_conds_transformation(thd, this); }
+  Item* varchar_upper_cmp_transformer(THD *thd, uchar *arg) override;
 };
 
 class Item_func_equal final :public Item_bool_rowready_func2
@@ -2632,6 +2633,7 @@ class Item_func_in :public Item_func_opt_neg,
   Item *in_predicate_to_in_subs_transformer(THD *thd, uchar *arg) override;
   Item *in_predicate_to_equality_transformer(THD *thd, uchar *arg) override;
   uint32 max_length_of_left_expr();
+  Item* varchar_upper_cmp_transformer(THD *thd, uchar *arg) override;
 };
 
 class cmp_item_row :public cmp_item
diff --git a/sql/opt_rewrite_remove_casefold.cc b/sql/opt_rewrite_remove_casefold.cc
new file mode 100644
index 0000000000000..bf45e1f00fea4
--- /dev/null
+++ b/sql/opt_rewrite_remove_casefold.cc
@@ -0,0 +1,148 @@
+#ifdef USE_PRAGMA_IMPLEMENTATION
+#pragma implementation				// gcc: Class implementation
+#endif
+
+#include "mariadb.h"
+#include "sql_priv.h"
+#include <m_ctype.h>
+#include "sql_partition.h"
+#include "sql_select.h"
+
+#include "opt_trace.h"
+
+/*
+  @brief
+    Check if passed item is "UCASE(table.colX)" where colX is either covered
+    by some index or is a part of partition expression.
+
+  @return
+     Argument of the UCASE if passed item matches
+     NULL otherwise.
+*/
+
+static Item* is_upper_key_col(Item *item)
+{
+  Item_func_ucase *item_func;
+  if ((item_func= dynamic_cast<Item_func_ucase*>(item)))
+  {
+    Item *arg= item_func->arguments()[0];
+    Item *arg_real= arg->real_item();
+    if (arg_real->type() == Item::FIELD_ITEM)
+    {
+      if (dynamic_cast<const Type_handler_longstr*>(arg_real->type_handler()))
+      {
+        Field *field= ((Item_field*)arg_real)->field;
+        bool appl= (field->flags & PART_KEY_FLAG);
+
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+        partition_info *part_info;
+        if (!appl && ((part_info= field->table->part_info)))
+        {
+          appl= bitmap_is_set(&part_info->full_part_field_set,
+                              field->field_index);
+        }
+#endif
+        if (appl)
+        {
+          /*
+            Make sure COERCIBILITY(UPPER(col))=COERCIBILITY(col)
+          */
+          DBUG_ASSERT(arg->collation.derivation ==
+                      item_func->collation.derivation);
+
+          /* Return arg, not arg_real. Do not walk into Item_ref objects */
+          return arg;
+        }
+      }
+    }
+  }
+  return nullptr;
+}
+
+
+static void trace_upper_removal_rewrite(THD *thd, Item *old_item, Item *new_item)
+{
+  Json_writer_object trace_wrapper(thd);
+  Json_writer_object obj(thd, "sargable_casefold_removal");
+  obj.add("before", old_item)
+     .add("after", new_item);
+}
+
+
+/*
+  @brief
+    Rewrite UPPER(key_varchar_col) = expr into key_varchar_col=expr
+
+  @detail
+    UPPER() may occur on both sides of the equality.
+    UCASE() is a synonym of UPPER() so we handle it, too.
+*/
+
+Item* Item_func_eq::varchar_upper_cmp_transformer(THD *thd, uchar *arg)
+{
+  if (cmp.compare_type() == STRING_RESULT &&
+      cmp.compare_collation()->state & MY_CS_UPPER_EQUAL_AS_EQUAL)
+  {
+    Item *arg0= arguments()[0];
+    Item *arg1= arguments()[1];
+    bool do_rewrite= false;
+    Item *tmp;
+
+    // Try rewriting the left argument
+    if ((tmp= is_upper_key_col(arguments()[0])))
+    {
+      arg0= tmp;
+      do_rewrite= true;
+    }
+
+    // Try rewriting the right argument
+    if ((tmp= is_upper_key_col(arguments()[1])))
+    {
+      arg1=tmp;
+      do_rewrite= true;
+    }
+
+    if (do_rewrite)
+    {
+      Item *res= new (thd->mem_root) Item_func_eq(thd, arg0, arg1);
+      if (res && !res->fix_fields(thd, &res))
+      {
+        trace_upper_removal_rewrite(thd, this, res);
+        return res;
+      }
+    }
+  }
+  return this;
+}
+
+
+/*
+  @brief
+    Rewrite "UPPER(key_col) IN (const-list)" into "key_col IN (const-list)"
+*/
+
+Item* Item_func_in::varchar_upper_cmp_transformer(THD *thd, uchar *arg)
+{
+  if (arg_types_compatible &&
+      m_comparator.cmp_type() == STRING_RESULT &&
+      cmp_collation.collation->state & MY_CS_UPPER_EQUAL_AS_EQUAL &&
+      all_items_are_consts(args + 1, arg_count - 1))
+  {
+    Item *arg0= arguments()[0];
+    Item *tmp;
+    if ((tmp= is_upper_key_col(arg0)))
+    {
+      Item_func_in *cl= (Item_func_in*)build_clone(thd);
+      Item *res;
+      cl->arguments()[0]= tmp;
+      cl->walk(&Item::cleanup_excluding_const_fields_processor, 0, 0);
+      res= cl;
+      if (res->fix_fields(thd, &res))
+        return this;
+      trace_upper_removal_rewrite(thd, this, res);
+      return res;
+    }
+  }
+  return this;
+}
+
diff --git a/sql/sql_delete.cc b/sql/sql_delete.cc
index ddd31ac700e95..a9be867932a14 100644
--- a/sql/sql_delete.cc
+++ b/sql/sql_delete.cc
@@ -476,6 +476,12 @@ bool Sql_cmd_delete::delete_from_single_table(THD *thd)
                                       (uchar *) 0);
   }
 
+  if (conds && optimizer_flag(thd, OPTIMIZER_SWITCH_SARGABLE_CASEFOLD))
+  {
+    conds= conds->top_level_transform(thd, &Item::varchar_upper_cmp_transformer,
+                                          (uchar *) 0);
+  }
+
 #ifdef WITH_PARTITION_STORAGE_ENGINE
   if (prune_partitions(thd, table, conds))
   {
diff --git a/sql/sql_priv.h b/sql/sql_priv.h
index d594238b80722..2ea86b5905eff 100644
--- a/sql/sql_priv.h
+++ b/sql/sql_priv.h
@@ -239,6 +239,7 @@
 #define OPTIMIZER_SWITCH_COND_PUSHDOWN_FROM_HAVING (1ULL << 34)
 #define OPTIMIZER_SWITCH_NOT_NULL_RANGE_SCAN       (1ULL << 35)
 #define OPTIMIZER_SWITCH_HASH_JOIN_CARDINALITY     (1ULL << 36)
+#define OPTIMIZER_SWITCH_SARGABLE_CASEFOLD         (1ULL << 37)
 
 #define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
                                   OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
@@ -270,7 +271,8 @@
                                   OPTIMIZER_SWITCH_USE_ROWID_FILTER | \
                                   OPTIMIZER_SWITCH_COND_PUSHDOWN_FROM_HAVING | \
                                   OPTIMIZER_SWITCH_OPTIMIZE_JOIN_BUFFER_SIZE |\
-                                  OPTIMIZER_SWITCH_HASH_JOIN_CARDINALITY)
+                                  OPTIMIZER_SWITCH_HASH_JOIN_CARDINALITY |\
+                                  OPTIMIZER_SWITCH_SARGABLE_CASEFOLD)
 /*
   Replication uses 8 bytes to store SQL_MODE in the binary log. The day you
   use strictly more than 64 bits by adding one more define above, you should
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 1061b3018cd00..d88bc2e25382c 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -2342,6 +2342,12 @@ JOIN::optimize_inner()
   if (thd->lex->are_date_funcs_used())
     transform_date_conds_into_sargable();
 
+  if (optimizer_flag(thd, OPTIMIZER_SWITCH_SARGABLE_CASEFOLD))
+  {
+    transform_all_conds_and_on_exprs(
+          thd, &Item::varchar_upper_cmp_transformer);
+  }
+
   conds= optimize_cond(this, conds, join_list, ignore_on_expr,
                        &cond_value, &cond_equal, OPT_LINK_EQUAL_FIELDS);
 
diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index 4eec441e9aaf5..15d65f12c9559 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -440,6 +440,12 @@ bool Sql_cmd_update::update_single_table(THD *thd)
                                       (uchar *) 0);
   }
 
+  if (conds && optimizer_flag(thd, OPTIMIZER_SWITCH_SARGABLE_CASEFOLD))
+  {
+    conds= conds->top_level_transform(thd, &Item::varchar_upper_cmp_transformer,
+                                          (uchar *) 0);
+  }
+
   // Don't count on usage of 'only index' when calculating which key to use
   table->covering_keys.clear_all();
   transactional_table= table->file->has_transactions_and_rollback();
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 49c58e60d75ad..93bbe5db3a2aa 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -2893,6 +2893,7 @@ export const char *optimizer_switch_names[]=
   "condition_pushdown_from_having",
   "not_null_range_scan",
   "hash_join_cardinality",
+  "sargable_casefold",
   "default", 
   NullS
 };
diff --git a/strings/ctype-utf8.c b/strings/ctype-utf8.c
index 121a3f945f6a1..bab804f16bddc 100644
--- a/strings/ctype-utf8.c
+++ b/strings/ctype-utf8.c
@@ -1243,7 +1243,8 @@ MY_CHARSET_HANDLER my_charset_utf8mb3_handler=
 struct charset_info_st my_charset_utf8mb3_general_ci=
 {
     33,0,0,             /* number       */
-    MY_CS_COMPILED|MY_CS_PRIMARY|MY_CS_STRNXFRM|MY_CS_UNICODE,  /* state  */
+    MY_CS_COMPILED|MY_CS_PRIMARY|MY_CS_STRNXFRM|MY_CS_UNICODE|
+      MY_CS_UPPER_EQUAL_AS_EQUAL,  /* state  */
     { charset_name_utf8mb3, charset_name_utf8mb3_length },            /* cs name */
     { STRING_WITH_LEN(MY_UTF8MB3 "_general_ci") },              /* name   */
     "",                 /* comment      */
@@ -3573,7 +3574,8 @@ MY_CHARSET_HANDLER my_charset_utf8mb4_handler=
 struct charset_info_st my_charset_utf8mb4_general_ci=
 {
   45,0,0,              /* number       */
-  MY_CS_COMPILED|MY_CS_PRIMARY|MY_CS_STRNXFRM|MY_CS_UNICODE|MY_CS_UNICODE_SUPPLEMENT,  /* state  */
+  MY_CS_COMPILED|MY_CS_PRIMARY|MY_CS_STRNXFRM|MY_CS_UNICODE|
+    MY_CS_UNICODE_SUPPLEMENT|MY_CS_UPPER_EQUAL_AS_EQUAL,  /* state  */
   { charset_name_utf8mb4, charset_name_utf8mb4_length}, /* cs name    */
   { STRING_WITH_LEN(MY_UTF8MB4_GENERAL_CI) },           /* name       */
   "UTF-8 Unicode",    /* comment      */