mysql - 如何在mysql中编写IF语句

Question

我有一张带type字段的桌子。

如何在查询中检查此字段：

type如果== 'a'我想检查一下

然后bes= amount, bed= '-'

否则bed= amount, bes= '-'

bes 和 bed 在我的表中并不存在，但数量是 (int)

这是我的尝试：

SELECT billing.*,
    CASE billing.type WHEN 'A' THEN billing.amount AS bes, '-' AS bed ELSE billing.amount AS bed, '-' AS bes END
    FROM billing

...我的搜索没有用

任何解决方案...

Answer 1

您可以为每一行创建条件，MySQL支持内联 IF语句。

SELECT billing.*,
       IF(billing.type = 'A', billing.amount, '-') AS bes,
       IF(billing.type = 'A', '-', billing.amount) AS bed
FROM   billing

Answer 2

为此，您需要两个 case 语句：

SELECT billing.*,
  CASE billing.type WHEN 'A' THEN billing.amount ELSE '-' AS bes END,
  CASE billing.type WHEN 'A' THEN '-' ELSE billing.amount AS bed END
FROM billing

Answer 3

一个CASE-WHEN-THEN-ELSE只能有一个返回值...

这应该可以解决问题：

SELECT billing.*,
CASE billing.type WHEN 'A' THEN billing.amount ELSE '-' END AS bes,
CASE billing.type WHEN 'A' THEN '-' ELSE billing.amount END AS bed 
FROM billing

Answer 4

SELECT billing.*,
    CASE  WHEN billing.type =  'A' THEN billing.amount ELSE 0 END AS bes,
    CASE  WHEN billing.type <> 'A' THEN billing.amount ELSE 0 END AS bed
FROM billing

Answer 5

根据您的 MySQL 版本，您可以使用IF或CASE CASE (1)、CASE (2)的两种不同语法之一。

SELECT *,
  (IF type = 'A' THEN amount ELSE '-' END IF) bes,
  (IF type = 'A' THEN '-' ELSE amount END IF) bed
FROM billing