如何在MySQL中使用UNION时知道结果来自哪个表

I'm using a union query:

我使用的是联合查询:

SELECT snippet_id, title FROM tbl_snippets WHERE title LIKE ?
UNION
SELECT tag_id, tag FROM tbl_tags WHERE tag LIKE ?
UNION
SELECT category_id, category FROM tbl_categories WHERE category LIKE ?
SELECT