id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	rc	ALL	NULL	CONSTRAINT_SCHEMA,TABLE_NAME	NULL	NULL	NULL	Using where; Open_full_table; Scanned 0 databases
1	SIMPLE	kcu	ALL	NULL	TABLE_SCHEMA,TABLE_NAME	NULL	NULL	NULL	Using where; Open_full_table; Scanned 0 databases; Using join buffer (Block Nested Loop)