没有子查询的左连接

Question

我得到以下输出，我想要相同的输出但没有子查询。我希望通过删除子查询来优化下面的查询，因为它会影响应用程序的性能。谁能帮我删除子查询并使用连接获取所需的数据。

SELECT DISTINCT rec.requestno as requestno
    , (SELECT min(dateandtime) 
       from recruitersubmission 
       where recruitersubmission.requestno = rec.requestno) as firstsubmsion
    , (SELECT max(dateandtime) 
       from recruitersubmission 
       where recruitersubmission.requestno = rec.requestno) as lastsubmission
    , cndinterview.dateandtime as  candidatefedtime
    , cndinterview.dateandtime AS recruitertime
    , CONCAT(availabledate,' ', availabletime) AS candidateavaibledatetime
    , cndfeedback.status AS status
    , cndfeedback.offereddate AS offereddate
    , cnd.status AS onboard
    , (SELECT COUNT(recruitersubmission.requestno)
       FROM recruitersubmission 
       WHERE recruitersubmission.requestno=rec.requestno) AS totalSub
    , (select COUNT(candidatefeedback.requestno) 
       from candidatefeedback 
       WHERE candidatefeedback.requestno = rec.requestno 
          && candidatefeedback.status = 'Selected' ) as totalsel
    , (select COUNT( candidatefeedback.requestno) 
       from candidatefeedback 
       WHERE candidatefeedback.requestno = rec.requestno 
          && cndfeedback.status = 'Rejected' ) as totalrej
    , (select COUNT(candidatefeedbkonboard.requestno) 
       from candidatefeedbkonboard 
       WHERE candidatefeedbkonboard.requestno = rec.requestno 
          && cnd.status = 'Drop' ) as totaldrop
    , (select COUNT(candidatefeedbkonboard.requestno) 
       from candidatefeedbkonboard 
       WHERE candidatefeedbkonboard.requestno = rec.requestno 
          && candidatefeedbkonboard.status = 'Onboarded' ) as totalonboard
from recruitersubmission AS rec 
LEFT JOIN candidatefeedbkonboard AS cnd 
    ON rec.requestno=cnd.requestno 
LEFT JOIN candidatefeedback AS cndfeedback 
    ON rec.requestno=cndfeedback.requestno 
LEFT JOIN candidatesinterview AS cndinterview 
    ON rec.requestno=cndinterview.requestno
where rec.clientname = '$client' 
   && rec.requestno != ''  
   && rec.country = '$location' 
   && date(rec.dateandtime) between '$fromdate'

我想避免下面这些子查询。

(select COUNT(candidatefeedback.requestno) 来自 candidatefeedback WHERE candidatefeedback.requestno = rec.requestno && candidatefeedback.status = 'Selected' ) as totalsel

Answer 1

感谢朋友们的帮助。我想出了怎么做。下面是解决方法供大家参考。

SELECT
    rec.requestno,
    COALESCE(totalsub, 0) AS totalsub,
    COALESCE(totalsel, 0) AS totalsel,
    COALESCE(totalrej, 0) AS totalrej
FROM recruitersubmission rec
LEFT JOIN (
    SELECT requestno, COUNT(*) AS totalsub
    FROM recruitersubmission
    GROUP BY requestno
) recruitersubmission  ON recruitersubmission.requestno = rec.requestno
LEFT JOIN (
    SELECT  requestno,count(if(status = 'Selected',1,Null)) AS totalsel,count(if(status = 'Rejected',1,Null)) as totalrej
    FROM candidatefeedback 
    GROUP BY requestno
) candidatefeedback  ON candidatefeedback.requestno = rec.requestno


GROUP by rec.requestno Limit 0,25

Answer 2

回复：您的子查询：

(SELECT 分钟(日期和时间) 来自招聘人员提交其中 recruitersubmission.requestno = rec.requestno)

需要INDEX(requestno, dateandtime)。对于其他子查询也是如此。

回复：Seejith 的回答：

count(if(status = 'Selected',1,Null))

可以替换为

SUM(status = 'Selected')

从而无需 COALESCE(.., 0)。

没有子查询的左连接

Left join Without Subqueries

mysql

sql

join

subquery

mariadb