case when 中如何使用計數

提示：兩種方法，一種是SUM(1)，一種是COUNT(column_name)

SUM(1)指的是：符合要求的返回1，然后case when外部用sum進行求和，

COUNT(column_name)指的是：符合要求的記錄一個唯一id，最后就相當於COUNT(id)

示例：

SELECT MIN(province_id) provinceNumber, MIN(province_name) provinceName,
               COUNT(project_id)                                                       a,
               SUM(this_issue_money)                                                   b,
               SUM(CASE
                       WHEN is_not_exit = true THEN
                           1
                   END)                                                                c,
               SUM(this_issue_money)                                                   d,
               SUM(CASE WHEN is_not_exit = true AND enterprise_type_id = 1 THEN 1 END) e,
               SUM(CASE
                       WHEN
                           enterprise_type_id = 1 THEN this_issue_money END)           f,
               SUM(CASE WHEN is_not_exit = true AND enterprise_type_id = 2 THEN 1 END) g,
               SUM(CASE
                       WHEN
                           enterprise_type_id = 2 THEN this_issue_money END)           h,
               SUM(CASE WHEN is_not_exit = true AND enterprise_type_id = 2 THEN 1 END) j,
               SUM(CASE
                       WHEN
                           enterprise_type_id = 2 THEN this_issue_money END)           k
        FROM l

換成COUNT，那么就是

select  COUNT(CASE WHEN is_not_exit = true then id) FROM L