mysqlのUnion Allの使い方

SELECT column_name(s) FROM table1 UNION ALL SELECT column_name(s) FROM table2;

-- 用union all去除结果后在用distinct排重，执行时间为：5.4秒 select DISTINCT xx.DO_DETAIL_ID from ( select do_detail_id from A union all select do_detail_id from B) xx;

-- 用union all去除结果后在用group by排重，执行时间为：5.69秒 select yy.DO_DETAIL_ID from ( select do_detail_id from A union all select do_detail_id from B) yy GROUP BY yy.DO_DETAIL_ID;