MDEV-32583 UUID() should be treated as stochastic for the purposes of forcing query materialization

RAND() and UUID() are treated differently with respect to subquery
materialization both should be marked as uncacheable, forcing materialization.
Altered Create_func_uuid(_short)::create_builder().
Added comment in header about UNCACHEABLE_RAND meaning also unmergeable.

Author: mariadb-RexJohnston

mysql-test/main/func_misc.result

@@ -1732,3 +1732,16 @@ RELEASE_ALL_LOCKS()
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA
 FROM information_schema.metadata_lock_info WHERE thread_id>0 ORDER BY TABLE_SCHEMA;
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA
+#
+# MDEV-32583 UUID() should be treated as stochastic for the purposes of
+#   forcing query materialization
+#
+create table t1 as WITH cte AS (SELECT UUID() as r  FROM seq_1_to_10)
+SELECT r as r1, r FROM cte;
+select count(*) from t1 where r1!=r;
+count(*)
+0
+drop table t1;
+#
+# End of 10.5 tests
+#

mysql-test/main/func_misc.test

@@ -1361,3 +1361,18 @@ FROM information_schema.metadata_lock_info WHERE thread_id>0 ORDER BY TABLE_SCHE
 
 --enable_ps2_protocol
 --enable_view_protocol
+
+--echo #
+--echo # MDEV-32583 UUID() should be treated as stochastic for the purposes of
+--echo #   forcing query materialization
+--echo #
+
+--source include/have_sequence.inc
+create table t1 as WITH cte AS (SELECT UUID() as r  FROM seq_1_to_10)
+SELECT r as r1, r FROM cte;
+select count(*) from t1 where r1!=r;
+drop table t1;
+
+--echo #
+--echo # End of 10.5 tests
+--echo #

sql/item_create.cc

@@ -5301,7 +5301,7 @@ Create_func_uuid::create_builder(THD *thd)
 {
   DBUG_ENTER("Create_func_uuid::create");
   thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
-  thd->lex->safe_to_cache_query= 0;
+  thd->lex->uncacheable(UNCACHEABLE_RAND);    // disallow cache and query merges
   DBUG_RETURN(new (thd->mem_root) Item_func_uuid(thd));
 }
 
@@ -5313,7 +5313,7 @@ Create_func_uuid_short::create_builder(THD *thd)
 {
   DBUG_ENTER("Create_func_uuid_short::create");
   thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
-  thd->lex->safe_to_cache_query= 0;
+  thd->lex->uncacheable(UNCACHEABLE_RAND);    // disallow cache and query merges
   DBUG_RETURN(new (thd->mem_root) Item_func_uuid_short(thd));
 }
 

sql/sql_lex.h

@@ -3621,6 +3621,15 @@ struct LEX: public Query_tables_list
     return (context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW);
   }
 
+  /**
+    Mark all queries in this lex structure as uncacheable for the cause given
+
+    @param cause    the reason queries are to be marked as uncacheable
+
+    Note, any cause is sufficient for st_select_lex_unit::can_be_merged() to
+    disallow query merges.
+  */
+
   inline void uncacheable(uint8 cause)
   {
     safe_to_cache_query= 0;

sql/sql_priv.h

@@ -316,7 +316,10 @@
 */
 /* This subquery has fields from outer query (put by user) */
 #define UNCACHEABLE_DEPENDENT_GENERATED   1
-/* This subquery contains functions with random result */
+/*
+  This subquery contains functions with random result.
+  Something that is uncacheable is by default unmergeable.
+*/
 #define UNCACHEABLE_RAND        2
 /* This subquery contains functions with side effect */
 #define UNCACHEABLE_SIDEEFFECT	4