Question

我有这个查询

SELECT `badges`.`id`,
       `badges`.`en_seo`

FROM   `badges`

WHERE  `status` IS  NULL
AND    `id`     NOT IN
       (SELECT `badges_id`

        FROM   `users_badges`

        WHERE  `users_id` = 1)

我可以使用JOINS重写此代码吗？

Answer 1

与查询完全等效的是：

SELECT    `badges`.`id`,
          `badges`.`en_seo`
FROM      `badges`
LEFT JOIN `users_badges`
       ON `badges`.`id` = `users_badges`.`badges_id`
      AND `users_badges`.`users_id` = 1
WHERE     `badges`.`status` IS NULL
  AND     `users_badges`.`users_id` IS NULL

然而，在Juan的回答中使用别名是一种常见的做法。

Answer 2

始终尝试为表名使用别名

SELECT b.`id`,
       b.`en_seo`
FROM   `badges` b
LEFT JOIN `users_badges` ub
  ON b.`id`= ub.`badges_id`
 and ub.`users_id` = 1
WHERE b.`status` IS  NULL
 AND ub.`id` IS NULL

使用JOIN而不是子查询

2 个答案: