'SELECT'语句中的'IF' – 根据列值select输出值
SELECT id, amount FROM report
如果report.type='P'
,则需要amount
为amount
,如果report.type='N'
-amount
。 我如何将这个添加到上面的查询?
SELECT id, IF(type = 'P', amount, amount * -1) as amount FROM report
请参阅http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html 。
此外,您可以处理条件为空时。 在空数量的情况下:
SELECT id, IF(type = 'P', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount FROM report
部分IFNULL(amount,0)
表示当金额不为空时返回金额,否则返回0 。
使用case
语句:
select id, case report.type when 'P' then amount when 'N' then -amount end as amount from `report`
SELECT CompanyName, CASE WHEN Country IN ('USA', 'Canada') THEN 'North America' WHEN Country = 'Brazil' THEN 'South America' ELSE 'Europe' END AS Continent FROM Suppliers ORDER BY CompanyName;
select id, case when report_type = 'P' then amount when report_type = 'N' then -amount else null end from table
最简单的方法是使用IF() 。 是的,Mysql允许你做条件逻辑。 IF函数需要3个参数条件,实际结果,错误结果。
所以逻辑是
if report.type = 'p' amount = amount else amount = -1*amount
SQL
SELECT id, IF(report.type = 'P', abs(amount), -1*abs(amount)) as amount FROM report
如果所有的no都是+ ve,你可以跳过abs()
SELECT id, amount FROM report WHERE type='P' UNION SELECT id, (amount * -1) AS amount FROM report WHERE type = 'N' ORDER BY id;
你也可以试试这个
Select id , IF(type=='p', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount from table
让我们试试这个。
SELECT id , IF(report.type == 'p', IFNULL(amount,0), IFNULL(amount,0) * -1) as amount FROM report