在TSQL中进行计数的最佳方法

Question

我在TSQL方面不太出色，我想以这种方式编写报告：

输入：表A

ID   Company Product  Flag
1    A        Car        Y
2    A        Van        N
3    B        Van        Y
4    A        Part       N

输出

Company     Y     N
A           1     2
B           1     0

如果可以协助TSQL ...

Answer 1

您可以使用条件聚合：

SELECT Company
    ,SUM(CASE WHEN Flag = 'Y' THEN 1 ELSE 0 END) AS Y
    ,SUM(CASE WHEN Flag = 'N' THEN 1 ELSE 0 END) AS N
FROM tab
GROUP BY Company

Answer 2

您正在寻找条件聚合：

select company,
       sum(case when flag = 'Y' then 1 else 0 end) as num_y,
       sum(case when flag = 'N' then 1 else 0 end) as num_n
from t
group by company;

Answer 3

您可以使用CASE表达式（人们称其为“ 条件聚合”）来按此计数每个客户的标记产品（当{{1} }列为空）：

Product

或者您可以使用此PIVOT查询，这是编写以上内容的一种简短形式：

SELECT Company
  , COUNT(CASE Flag WHEN 'Y' THEN Product END) AS Y
  , COUNT(CASE Flag WHEN 'N' THEN Product END) AS N
FROM YourTable
GROUP BY Company;

Answer 4

用例何时

    select company,
   sum(case when flag='Y' then 1 else 0 end) as Y,
   sum(case when flag='N' then 1 else 0 end) as N from tabe_data
   group by company