单表中的多个Where子句选择查询

Question

朋友们，我有一张金额和税金的表格如下

表1

Amount        tax
200            5
300            2
100           12
 50            5
200           12

在上表中，我有amount列和tax，这里我想要与tax子句的总金额

例如sum(amount) where tax='2'，sum(amount) where tax='5'和sum(amount) where tax='12'

我希望输出像

    amount_2 | tax_2 | amount_5 | tax_5 | amount_12 | tax_12
----------------------------------------------------------
    300      |  2    | 250      |  5    |   300     | 12

Answer 1

您可以为条件和

编写如下内容

select 
sum(case when tax = 2 then amount else 0 end) amount_2,
2 as tax_2,
sum(case when tax = 5 then amount else 0 end) amount_5,
5 as tax_5,
sum(case when tax = 12 then amount else 0 end) amount_12,
12 as tax_12
from table
 /* group by somecol if needed sum per group*/