'SELECT' 语句中的 'IF' - 根据列值选择输出值
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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