Question

请在不使用mysql中的子查询

的情况下将以下查询转换为连接查询

SELECT u.id, u.name, u.avatar, u.slug, u.location
FROM user_registration as u
WHERE u.id <>'3' AND u.id NOT IN (SELECT f.user_id FROM followers as f WHERE f.follower_id ='3')
order by id

Answer 1

将查询移植到联接的一种方法是在user_registration上使用子查询离开加入followers。要保留的记录的条件是用户注册ID不是'3'，并且该记录与followers上的子查询的连接中的任何内容都不匹配。

SELECT t1.id, t1.name, t1.avatar, t1.slug, t1.location
FROM user_registration t1
LEFT JOIN
(
    SELECT f.user_id
    FROM followers f
    WHERE f.follower_id = '3'
) t2
    ON t1.id = t2.user_id
WHERE t1.id <> '3' AND t2.user_id IS NULL
ORDER BY t1.id

我认为以下查询也应该有效：

SELECT t1.id, t1.name, t1.avatar, t1.slug, t1.location
FROM user_registration t1
LEFT JOIN followers t2
    ON t1.id = t2.user_id AND t2.follower_id = '3'
WHERE t1.id <> '3' AND t2.user_id IS NULL
ORDER BY t1.id

Answer 2

这是一个不使用子选择的连接查询：

SELECT
    u.id, u.name, u.avatar, u.slug, u.location
FROM
    user_registration u
    LEFT JOIN followers f ON (u.id = f.user_id AND f.follower_id = 3)
WHERE
    u.id <>'3' AND
    f.user_id IS NULL
ORDER BY id

请注意，如果您使用子选择（如少数其他答案），即使您正在加入其结果，MySQL仍可能使用内部临时表（缺少任何索引）来执行连接。如果您加入实际表，则保留使用现有索引加入的所有好处。您始终可以运行EXPLAIN以查看正在使用的索引。

Answer 3

SELECT u.id, u.name, u.avatar, u.slug, u.location
FROM user_registration as u
LEFT JOIN followers ON followers.follower._id = u.id
AND u.id <>'3'

Answer 4

这可能有效

 SELECT u.id, u.name, u.avatar, u.slug, u.location
    FROM user_registration u LEFT JOIN followers f
    ON u.id=f.user_id
    WHERE u.id <>'3' AND f.follower_id <>'3'
    order by u.id;

如何将此查询转换为连接查询

4 个答案: