Question

我有一个非常简单的查询：

 SELECT users.id, COUNT(others.id) as c
 FROM users JOIN other ON users.id=others.user_id 
 GROUP BY users.id

我想要做的是在c时用''替换c=0中的号码。

例如，而不是像

这样的行

 # I have this
 1, 0
 2, 1

 # I want c=0 replaced with ''
 1, ''  
 2, 1

我如何在MySQL中执行此操作？

Answer 1

试试这个：

SELECT users.id, IF(COUNT(others.id) = 0, '', COUNT(others.id)) as c
FROM users JOIN other ON users.id=others.user_id 
GROUP BY users.id

Answer 2

使用CASE or IF

SELECT t.id, CASE t.c = 0 THEN '' ELSE t.c FROM (
    SELECT users.id as id, COUNT(others.id) as c
    FROM users JOIN other ON users.id=others.user_id 
    GROUP BY users.id
 ) as t

Answer 3

你可以试试这个：

SELECT users.id, IF(COUNT(others.id) > 0, COUNT(others.id), "''") as c
FROM users JOIN other ON users.id=others.user_id 
GROUP BY users.id

或者有COALESCE但是如果不能使用0结果

“''”（2个双引号中的2个单引号）会给你

1，''而不是

1，

根据计数结果选择不同的数据

3 个答案: