Question

我有这个mysql可行，但我不禁想到有更好的方法吗？

SELECT u.username, count( c.username ) AS intImageCount
FROM users u
JOIN content c ON c.username = u.username
WHERE (SELECT count( username )FROM content WHERE username = c.username) > 0
GROUP BY u.username

有什么建议吗？

Answer 1

尝试使用HAVING而不是

像

这样的东西

SELECT u.username, count( c.username ) AS intImageCount 
FROM users u 
JOIN content c ON c.username = u.username 
GROUP BY u.username
HAVING count( c.username ) > 0

查看SELECT Syntax

Answer 2

而不是HAVING，你的(INNER) JOIN已经成功了您可以完全删除子查询。

SELECT   u.username
         , count( c.username ) AS intImageCount
FROM     users u
         INNER JOIN content c ON c.username = u.username
GROUP BY u.username

Answer 3

您没有看到子选择的需要并使用LEFT JOIN：

SELECT u.username, count( c.username ) AS intImageCount
FROM users u
LEFT JOIN content c ON c.username = u.username
GROUP BY u.username

一个更有效的MySQL语句？

3 个答案: