'SELECT' 语句中的 'IF' - 根据列值选择输出值

2021-11-20 00:00:00 sql database mysql 
SELECT id, amount FROM report

如果 report.type='P' 和 -amount 如果 <代码>report.type='N'.如何将其添加到上述查询中?

I need amount to be amount if report.type='P' and -amount if report.type='N'. How do I add this to the above query?

推荐答案

SELECT id, 
       IF(type = 'P', amount, amount * -1) as amount
FROM report

见http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.

此外，您可以在条件为空时进行处理.在金额为空的情况下:

Additionally, you could handle when the condition is null. In the case of a null amount:

SELECT id, 
       IF(type = 'P', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount
FROM report

IFNULL(amount,0)部分表示当金额不为空时返回金额，否则返回0.

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