SQL：如何在两个不同的条件上求和相同的值

Question

可以说，我有下表记录了谁投资了公司列表。

Table: corporate_investments

company investor investment date
--------------------------------
CorpA    Alice     10       12/1
CorpB    Bob       20       12/2
CorpB    Sally     20       12/3 
CorpC    Cathy     30       12/4
CorpC    Alice     40       12/5
CorpC    Bob       10       12/6
CorpC    Bob       20       12/7

我将如何运行一个查询，以返回每个公司，鲍勃（VIP）的总投资以及对该公司的总投资？

我试过了

SELECT company,SUM(investment) as total investment
FROM corporate_investments
GROUP BY company

成功找到总投资额。

company    total_investment
---------------------------
CorpA           10
CorpB           40
CorpC          100

现在，我想为每个公司添加Bob的总金额。 我在SUM（）函数本身内部需要类似子句的内容，但对如何执行此操作感到困惑。

Answer 1

使用条件聚合：

SELECT company, SUM(investment) as total,
       sum(case when investor = 'Bob' then investment else 0 end) as BobTotal
FROM corporate_investments
GROUP BY company;

Answer 2

您可以使用WITH ROLLUP获得每个投资者的滚动总额：

SELECT company, investor, SUM(investment) AS total
FROM corporate_investments
GROUP BY company, investor WITH ROLLUP

这将产生如下所示：

CorpA    Alice     10
CorpA    NULL      10
CorpB    Bob       20
CorpB    Sally     20
CorpB    NULL      40
CorpC    Alice     40
CorpC    Bob       30
CorpC    Cathy     30
CorpC    NULL     100