MDEV-24346 valgrind error in main.precedence

in queries like

  create view v1 as select 2 like 1 escape (3 in (select 0 union select 1));
  select 2 union select * from v1;

Item_func_like::escape was left uninitialized, because
Item_in_optimizer is const_during_execution()
but not actually const_item() during execution.

It's not, because const subquery evaluation was disabled for derived.
Practically it only needs to be disabled for multi-update
that runs fix_fields() before all tables are locked.

mysql-test/suite/innodb/r/innodb_multi_update.result

@@ -81,4 +81,5 @@ CREATE TABLE t1(f1 INT) ENGINE=INNODB;
 INSERT INTO t1 VALUES(1);
 UPDATE (SELECT ((SELECT 1 FROM t1), 1) FROM t1 WHERE (SELECT 1 FROM t1)) x, (SELECT 1) AS d SET d.f1 = 1;
 ERROR 21000: Operand should contain 1 column(s)
+UPDATE (SELECT ((SELECT 1 FROM t1),1) = (1,1) FROM t1 WHERE (SELECT 1 FROM t1)) x, t1 AS d SET d.f1 = 1;
 DROP TABLE t1;

mysql-test/suite/innodb/t/innodb_multi_update.test

@@ -35,4 +35,5 @@ CREATE TABLE t1(f1 INT) ENGINE=INNODB;
 INSERT INTO t1 VALUES(1);
 --error ER_OPERAND_COLUMNS
 UPDATE (SELECT ((SELECT 1 FROM t1), 1) FROM t1 WHERE (SELECT 1 FROM t1)) x, (SELECT 1) AS d SET d.f1 = 1;
+UPDATE (SELECT ((SELECT 1 FROM t1),1) = (1,1) FROM t1 WHERE (SELECT 1 FROM t1)) x, t1 AS d SET d.f1 = 1;
 DROP TABLE t1;

sql/item_cmpfunc.cc

@@ -5261,6 +5261,7 @@ void Item_func_like::print(String *str, enum_query_type query_type)
 longlong Item_func_like::val_int()
 {
   DBUG_ASSERT(fixed == 1);
+  DBUG_ASSERT(escape != -1);
   String* res= args[0]->val_str(&cmp_value1);
   if (args[0]->null_value)
   {
@@ -5352,10 +5353,13 @@ bool fix_escape_item(THD *thd, Item *escape_item, String *tmp_str,
     my_error(ER_WRONG_ARGUMENTS,MYF(0),"ESCAPE");
     return TRUE;
   }
-  
+
+  IF_DBUG(*escape= -1,);
+
   if (escape_item->const_item())
   {
     /* If we are on execution stage */
+    /* XXX is it safe to evaluate is_expensive() items here? */
     String *escape_str= escape_item->val_str(tmp_str);
     if (escape_str)
     {

sql/sql_derived.cc

@@ -738,14 +738,12 @@ bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived)
       !(derived->derived_result= new (thd->mem_root) select_union(thd)))
     DBUG_RETURN(TRUE); // out of memory
 
-  lex->context_analysis_only|= CONTEXT_ANALYSIS_ONLY_DERIVED;
   // st_select_lex_unit::prepare correctly work for single select
   if ((res= unit->prepare(thd, derived->derived_result, 0)))
     goto exit;
   if (derived->with &&
       (res= derived->with->rename_columns_of_derived_unit(thd, unit)))
     goto exit; 
-  lex->context_analysis_only&= ~CONTEXT_ANALYSIS_ONLY_DERIVED;
   if ((res= check_duplicate_names(thd, unit->types, 0)))
     goto exit;
 

sql/sql_update.cc

@@ -1534,7 +1534,11 @@ int mysql_multi_update_prepare(THD *thd)
     During prepare phase acquire only S metadata locks instead of SW locks to
     keep prepare of multi-UPDATE compatible with concurrent LOCK TABLES WRITE
     and global read lock.
+
+    Don't evaluate any subqueries even if constant, because
+    tables aren't locked yet.
   */
+  lex->context_analysis_only|= CONTEXT_ANALYSIS_ONLY_DERIVED;
   if (thd->lex->sql_command == SQLCOM_UPDATE_MULTI)
   {
     if (open_tables(thd, &table_list, &table_count,
@@ -1557,6 +1561,9 @@ int mysql_multi_update_prepare(THD *thd)
   {
     DBUG_RETURN(TRUE);
   }
+
+  lex->context_analysis_only&= ~CONTEXT_ANALYSIS_ONLY_DERIVED;
+
   (void) read_statistics_for_tables_if_needed(thd, table_list);
   /* @todo: downgrade the metadata locks here. */