MYSQL 在子查询后插入计数

2022-01-23 00:00:00 subquery insert mysql nested-queries

我正在尝试将一些数据插入到表中，但仅当子查询 COUNT 大于 0 时.

I'm trying to INSERT some data into a table but only when the subquery COUNT is > 0.

这是我目前所拥有的.

INSERT INTO users_friends (userId, friendId) VALUES (77, 100) 
WHERE 
(SELECT COUNT(id) FROM users WHERE email = 'a@g.com') > 0

这两个查询独立工作，仅供参考.

Both queries work independently FYI.

希望这应该是一个简单的修复.干杯

This should be a simple fix hopefully. Cheers

推荐答案

SQLFiddle 演示如果有记录'a@g.com'

SQLFiddle 演示，如果没有记录 'a@g.com'p>

INSERT INTO users_friends (userId, friendId) 
SELECT 77, 100 
FROM users WHERE email = 'a@g.com' LIMIT 1;

另一种方法是:

INSERT INTO users_friends (userId, friendId) 
SELECT 77, 100 
FROM dual
WHERE EXISTS
      ( SELECT * FROM users WHERE email = 'a@g.com' ) ;

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