MDEV-12489 The select stmt may fail due to "having clause is ambiguou…

…s" unexpected

only compare field references with an alias (from the SELECT clause)
when this reference doesn't specify an explicit table name part.

mysql-test/r/group_by.result

@@ -2545,3 +2545,8 @@ select
 from t4;
 ERROR 42S22: Reference 'field7' not supported (reference to group function)
 drop table t1, t2, t3, t4;
+create table t1 (c1 int, c2 int);
+create table t2 (c1 int, c2 int);
+select t1.c1 as c1, t2.c2 as c1 from t1, t2 where t1.c1 < 20 and t2.c2 > 5 group by t1.c1, t2.c2 having t1.c1 < 3;
+c1	c1
+drop table t1, t2;

mysql-test/t/group_by.test

@@ -1722,6 +1722,14 @@ select
 from t4;
 drop table t1, t2, t3, t4;
 
+#
+# MDEV-12489 The select stmt may fail due to "having clause is ambiguous" unexpected
+#
+create table t1 (c1 int, c2 int);
+create table t2 (c1 int, c2 int);
+select t1.c1 as c1, t2.c2 as c1 from t1, t2 where t1.c1 < 20 and t2.c2 > 5 group by t1.c1, t2.c2 having t1.c1 < 3;
+drop table t1, t2;
+
 #
 # End of MariaDB 5.5 tests
 #

sql/item.cc

@@ -4622,7 +4622,7 @@ static Item** find_field_in_group_list(Item *find_item, ORDER *group_list)
     int cur_match_degree= 0;
 
     /* SELECT list element with explicit alias */
-    if ((*(cur_group->item))->name &&
+    if ((*(cur_group->item))->name && !table_name &&
         !(*(cur_group->item))->is_autogenerated_name &&
         !my_strcasecmp(system_charset_info,
                        (*(cur_group->item))->name, field_name))