| 用途 | 结果集纵向合并 |
|---|---|
| 语法 | SELECT … UNION [ALL] SELECT … |
| 差异 | UNION 去重，UNION ALL 不去重 |
用法示例
用法示例
SELECT id, 'order' AS src FROM orders WHERE created_at >= CURDATE()
UNION ALL
SELECT id, 'refund' AS src FROM refunds WHERE created_at >= CURDATE();排序位置
排序位置
(SELECT id FROM t1 LIMIT 10)
UNION ALL
(SELECT id FROM t2 LIMIT 10)
ORDER BY id DESC LIMIT 20;UNION 去重会对合并结果做唯一化（可能用临时表），能接受重复建议一律用 UNION ALL。