在同一选择语句中计算具有不同条件的相同 id 列

Posted 2023-02-24

【中文标题】在同一选择语句中计算具有不同条件的相同 id 列

【英文标题】：Count same id column with different condition in same select statement

【发布时间】：2014-01-19 20:48:35

【问题描述】：

我需要将两个选择语句合并为一个选择

SELECT count(tbl_employer_post_details.employer_id) pending
  FROM tbl_employer_post_details, 
       tbl_employer_registration
 WHERE job_status=0 
   AND tbl_employer_registration.employer_id = 
                                   tbl_employer_post_details.employer_id
 LIMIT start,max;

第二个查询，唯一的区别是WHERE job_status=1：

SELECT count(tbl_employer_post_details.employer_id) approved
  FROM tbl_employer_post_details, 
       tbl_employer_registration
 WHERE job_status=1 
   AND tbl_employer_registration.employer_id = 
                         tbl_employer_post_details.employer_id
  LIMIT start,max;

【问题讨论】：

您是要合并计数（例如，员工总数为 5 人，任何一种状态），还是分开（2 人的工作状态为 0，3 人的工作状态为 1）？

【参考方案1】：

SELECT count(tbl_employer_post_details.employer_id) PostDetails
FROM tbl_employer_post_details, tbl_employer_registration
WHERE job_status IN(0,1) AND  
tbl_employer_registration.employer_id=tbl_employer_post_details.employer_id LIMIT start,max;

SELECT SUM(job_status = 0) pending,
       SUM(job_status = 1) approved
FROM tbl_employer_post_details, tbl_employer_registration
WHERE job_status IN(0,1) AND  
tbl_employer_registration.employer_id=tbl_employer_post_details.employer_id LIMIT start,max;

【讨论】：

我想他想要返回 2 列？

【参考方案2】：

这样试试吧。

  SELECT SUM(case when job_status = 0 then 1 else 0 end) pending,
         SUM(case when job_status = 1 then 1 else 0 end) approved
  FROM tbl_employer_post_details d JOIN tbl_employer_registration r
    ON r.employer_id = d.employer_id
 WHERE job_status IN (0, 1)

【参考方案3】：

试试这个：

SELECT SUM(job_status = 0) pending, SUM(job_status = 1) approved 
FROM tbl_employer_post_details epd 
INNER JOIN tbl_employer_registration er ON epd.employer_id = er.employer_id
WHERE job_status IN (0, 1);

【参考方案4】：

试试这个方法

SELECT SUM(job_status = 0) pending,
       SUM(job_status = 1) approved
  FROM tbl_employer_post_details d JOIN tbl_employer_registration r
    ON r.employer_id = d.employer_id
 WHERE job_status IN (0, 1)