mysql - SQL 条件连接挑战

Question

我在 mysql 数据库中有 2 个表存储和共享。我试图避免 IN 子句。请参阅下文了解更多详情

select id, user_id from stores where user_id =7;
+----+---------+
| id | user_id |
+----+---------+
| 36 |       7 |
| 37 |       7 |


select stores_id,share_id from shares where share_id=7;
+-----------+----------+
| stores_id | share_id |
+-----------+----------+
|        15 |        7 |
|        38 |        7 |

现在我运行这个

SELECT stores.id
FROM   stores
WHERE  user_id = 7
UNION
(SELECT stores.id
 FROM   stores
 WHERE  id IN (SELECT stores_id
               FROM   shares
               WHERE  share_id = 7)); 

要得到以下结果:

+----+
| id |
+----+
| 36 |
| 37 |
| 15 |
| 38 |
+----+

问题 如何重写查询以便不使用 IN 关键字。？

Answer 1

您可以使用EXISTS:

WHERE EXISTS
       ( SELECT 1
           FROM shares
          WHERE share_id = 7
            AND stores_id = stores.id
       )

或加入:

JOIN shares
  ON shares.stores_id = stores.id
 AND shares.share_id = 7

(请注意，JOIN 可能会返回某些存储的多个副本，但由于 UNION 暗示 SELECT DISTINCT，因此实际上不会影响您的最终结果集。)