是否可以在Count()中指定一个条件?我希望只计算在Position列中有“Manager”的行。

我想在count语句中做,而不是用WHERE;我正在询问它,因为我需要在相同的SELECT(类似count (Position = Manager), count (Position = Other))中计算经理和其他,所以在这个例子中,WHERE对我来说没有用处。


当前回答

假设你不想限制返回的行,因为你也在聚合其他值,你可以这样做:

select count(case when Position = 'Manager' then 1 else null end) as ManagerCount
from ...

假设在同一列中,你有经理,主管和团队领导的值,你可以得到每一个的计数如下所示:

select count(case when Position = 'Manager' then 1 else null end) as ManagerCount,
    count(case when Position = 'Supervisor' then 1 else null end) as SupervisorCount,
    count(case when Position = 'Team Lead' then 1 else null end) as TeamLeadCount,
from ...

其他回答

这取决于你的意思,但另一种解释的意思是,你想要计算具有特定值的行,但不想将SELECT限制为只是那些行…

你可以使用SUM()和一个子句,像这样而不是使用COUNT(): 如。

SELECT SUM(CASE WHEN Position = 'Manager' THEN 1 ELSE 0 END) AS ManagerCount,
    SUM(CASE WHEN Position = 'CEO' THEN 1 ELSE 0 END) AS CEOCount
FROM SomeTable

如果使用Postgres或SQLite,可以使用Filter子句来提高可读性:

SELECT
  COUNT(1) FILTER (WHERE POSITION = 'Manager') AS ManagerCount,
  COUNT(1) FILTER (WHERE POSITION = 'Other') AS OtherCount
FROM ...

BigQuery也有Countif -在这里可以看到不同SQL方言对这些特性的支持: https://modern-sql.com/feature/filter

SELECT COUNT(*) FROM bla WHERE Position = 'Manager'

如果使用SQL 2005或更高版本,也可以使用Pivot关键字

更多信息来自Technet

SELECT *
FROM @Users
PIVOT (
    COUNT(Position)
    FOR Position
    IN (Manager, CEO, Employee)
) as p

测试数据集

DECLARE @Users TABLE (Position VARCHAR(10))
INSERT INTO @Users (Position) VALUES('Manager')
INSERT INTO @Users (Position) VALUES('Manager')
INSERT INTO @Users (Position) VALUES('Manager')
INSERT INTO @Users (Position) VALUES('CEO')
INSERT INTO @Users (Position) VALUES('Employee')
INSERT INTO @Users (Position) VALUES('Employee')
INSERT INTO @Users (Position) VALUES('Employee')
INSERT INTO @Users (Position) VALUES('Employee')
INSERT INTO @Users (Position) VALUES('Employee')
INSERT INTO @Users (Position) VALUES('Employee')

我认为您可以使用一个简单的WHERE子句来只选择count some记录。