MDEV-6046: MySQL Bug#11766684 59851: UNINITIALISED VALUE IN...

MDEV-6046: MySQL Bug#11766684 59851: UNINITIALISED VALUE IN ITEM_FUNC_LIKE::SELECT_OPTIMIZE WITH SUBQUERY AND

mysql-test/r/func_str.result

@@ -2658,6 +2658,17 @@ group_concat( i )	field
 NULL	NULL
 8	
 drop table t1;
+#
+# Bug#11766684 59851: UNINITIALISED VALUE IN ITEM_FUNC_LIKE::SELECT_OPTIMIZE WITH SUBQUERY AND
+#
+CREATE TABLE t2(a INT, KEY(a));
+INSERT INTO t2 VALUES (1),(2);
+CREATE TABLE t1(b INT, PRIMARY KEY(b));
+INSERT INTO t1 VALUES (0),(254);
+SELECT 1 FROM t2 WHERE a LIKE
+(SELECT  EXPORT_SET(1, b, b, b, b) FROM t1 LIMIT 1);
+1
+DROP TABLE t1, t2;
 End of 5.1 tests
 #
 # Start of 5.3 tests

mysql-test/t/func_str.test

@@ -1407,6 +1407,18 @@ insert into t1 values (null),(8);
 select group_concat( i ), make_set( i, 'a', 'b' ) field from t1 group by field;
 drop table t1;
 
+--echo #
+--echo # Bug#11766684 59851: UNINITIALISED VALUE IN ITEM_FUNC_LIKE::SELECT_OPTIMIZE WITH SUBQUERY AND
+--echo #
+
+CREATE TABLE t2(a INT, KEY(a));
+INSERT INTO t2 VALUES (1),(2);
+CREATE TABLE t1(b INT, PRIMARY KEY(b));
+INSERT INTO t1 VALUES (0),(254);
+SELECT 1 FROM t2 WHERE a LIKE
+(SELECT  EXPORT_SET(1, b, b, b, b) FROM t1 LIMIT 1);
+DROP TABLE t1, t2;
+
 --echo End of 5.1 tests
 
 --echo #

sql/item_cmpfunc.cc

@@ -4896,21 +4896,20 @@ longlong Item_func_like::val_int()
 
 Item_func::optimize_type Item_func_like::select_optimize() const
 {
-  if (args[1]->const_item() && !args[1]->is_expensive())
-  {
-    String* res2= args[1]->val_str((String *)&cmp.value2);
-    const char *ptr2;
+  if (!args[1]->const_item() || args[1]->is_expensive())
+    return OPTIMIZE_NONE;
 
-    if (!res2 || !(ptr2= res2->ptr()))
+  String* res2= args[1]->val_str((String *)&cmp.value2);
+  if (!res2)
     return OPTIMIZE_NONE;
 
-    if (*ptr2 != wild_many)
-    {
-      if (args[0]->result_type() != STRING_RESULT || *ptr2 != wild_one)
+  if (!res2->length()) // Can optimize empty wildcard: column LIKE ''
     return OPTIMIZE_OP;
-    }
-  }
-  return OPTIMIZE_NONE;
+
+  DBUG_ASSERT(res2->ptr());
+  char first= res2->ptr()[0];
+  return (first == wild_many || first == wild_one) ?
+    OPTIMIZE_NONE : OPTIMIZE_OP;
 }