Mysql Select 带有 case 语句和字段比较

Question

我正在从具有字段比较值的表中进行选择，例如

Select FieldA,FieldB,(FieldC-FIeldD) as Difference

现在想要实际选择差异字段的值，例如

When Difference=0 then 'North'
When Different>0 and Difference<=90 then 'NorthEast'
When Difference=90 then 'South'

等等，但我无法将其插入到选择中。我已经在更新中成功完成了此操作，但“选择”却逃脱了我

Answer 1

我认为子选择查询在这里效果很好。

目前您的声明如下:

Select FieldA,FieldB,(FieldC-FIeldD) as Difference from <TABLE>

相反，您可以将其放在子选择中，如下所示:

select * from 
(
Select FieldA,FieldB,(FieldC-FIeldD) as Difference from <TABLE>
) sub_table

现在您可以在最外面的 select 语句中执行 case 语句:

select 
CASE
    When Difference=0 then 'North'
    When Difference>0 and Difference<=90 then 'NorthEast'
    When Difference=90 then 'South'
END as answer
from 
(
Select FieldA,FieldB,(FieldC-FIeldD) as Difference from <TABLE>
)