MDEV-22719 Long unique keys are not created when individual key_part->length <...

MDEV-22719 Long unique keys are not created when individual key_part->length < max_key_length but SUM(key_parts->length) > max_key_length

Make UNIQUE HASH key in case when key_info->key_length > max_key_length

mysql-test/main/long_unique_bugs.result

@@ -277,3 +277,14 @@ create table t2(id int primary key, a blob, b varchar(20) as (LEFT(a,2)));
 INSERT INTO t2 VALUES (1, 'foo', default);
 DROP TABLE t1, t2;
 SET binlog_row_image= FULL;
+CREATE TABLE t1 (a int, b VARCHAR(1000), UNIQUE (a,b)) ENGINE=MyISAM;
+show index from t1;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment
+t1	0	a	1	a	A	NULL	NULL	NULL	YES	HASH		
+t1	0	a	2	b	A	NULL	NULL	NULL	YES	HASH		
+CREATE TABLE t2 (a varchar(900), b VARCHAR(900), UNIQUE (a,b)) ENGINE=MyISAM;
+show index from t2;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment
+t2	0	a	1	a	A	NULL	NULL	NULL	YES	HASH		
+t2	0	a	2	b	A	NULL	NULL	NULL	YES	HASH		
+DROP TABLE t1,t2;

mysql-test/main/long_unique_bugs.test

@@ -356,3 +356,15 @@ INSERT INTO t2 VALUES (1, 'foo', default);
 # Cleanup
 DROP TABLE t1, t2;
 SET binlog_row_image= FULL;
+
+#
+# MDEV-22719 Long unique keys are not created when individual key_part->length < max_key_length but SUM(key_parts->length) > max_key_length
+#
+
+CREATE TABLE t1 (a int, b VARCHAR(1000), UNIQUE (a,b)) ENGINE=MyISAM;
+show index from t1;
+CREATE TABLE t2 (a varchar(900), b VARCHAR(900), UNIQUE (a,b)) ENGINE=MyISAM;
+show index from t2;
+
+# Cleanup
+DROP TABLE t1,t2;

sql/sql_table.cc

@@ -4168,6 +4168,8 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
     if (key->type == Key::UNIQUE && !(key_info->flags & HA_NULL_PART_KEY))
       unique_key=1;
     key_info->key_length=(uint16) key_length;
+    if (key_info->key_length > max_key_length && key->type == Key::UNIQUE)
+      is_hash_field_needed= true;
     if (key_length > max_key_length && key->type != Key::FULLTEXT &&
         !is_hash_field_needed)
     {