Fixed mdev-14237 Server crash on query with regexp_substr

It's better to prohibit pushdown of conditions that involve
regexp_substr() and regexp_replace() into materialized derived
tables / views until proper implementations of the get_copy()
virtual method are provided for those functions.

mysql-test/r/derived_cond_pushdown.result

@@ -8766,3 +8766,44 @@ EXPLAIN
 }
 DROP VIEW v2;
 DROP TABLE t1,t2;
+#
+# MDEV-14237: derived with regexp_substr() in select list
+#
+create table t1 (a char(8));
+insert into t1 values ('b'), ('a'), ('xx');
+select *
+from ( select distinct regexp_substr(t1.a,'^[A-Za-z]+') as f from t1) as t
+where t.f = 'a' or t.f = 'b';
+f
+b
+a
+explain format=json select *
+from ( select distinct regexp_substr(t1.a,'^[A-Za-z]+') as f from t1) as t
+where t.f = 'a' or t.f = 'b';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived2>",
+      "access_type": "ALL",
+      "rows": 3,
+      "filtered": 100,
+      "attached_condition": "t.f = 'a' or t.f = 'b'",
+      "materialized": {
+        "query_block": {
+          "select_id": 2,
+          "temporary_table": {
+            "table": {
+              "table_name": "t1",
+              "access_type": "ALL",
+              "rows": 3,
+              "filtered": 100
+            }
+          }
+        }
+      }
+    }
+  }
+}
+drop table t1;

mysql-test/t/derived_cond_pushdown.test

@@ -1548,3 +1548,20 @@ eval explain format=json $q;
 
 DROP VIEW v2;
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-14237: derived with regexp_substr() in select list
+--echo #
+
+create table t1 (a char(8));
+insert into t1 values ('b'), ('a'), ('xx');
+
+let $q=
+select *
+from ( select distinct regexp_substr(t1.a,'^[A-Za-z]+') as f from t1) as t
+where t.f = 'a' or t.f = 'b';
+
+eval $q;
+eval explain format=json $q;
+
+drop table t1;

sql/item_strfunc.h

@@ -333,8 +333,7 @@ class Item_func_regexp_replace :public Item_str_func
   bool fix_fields(THD *thd, Item **ref);
   void fix_length_and_dec();
   const char *func_name() const { return "regexp_replace"; }
-  Item *get_copy(THD *thd, MEM_ROOT *mem_root)
-  { return get_item_copy<Item_func_regexp_replace>(thd, mem_root, this); }
+  Item *get_copy(THD *thd, MEM_ROOT *mem_root) { return 0;}
 };
 
 
@@ -356,8 +355,7 @@ class Item_func_regexp_substr :public Item_str_func
   bool fix_fields(THD *thd, Item **ref);
   void fix_length_and_dec();
   const char *func_name() const { return "regexp_substr"; }
-  Item *get_copy(THD *thd, MEM_ROOT *mem_root)
-  { return get_item_copy<Item_func_regexp_substr>(thd, mem_root, this); }
+  Item *get_copy(THD *thd, MEM_ROOT *mem_root) { return 0; }
 };