Question

这里我加入两个表，这段代码无法获得c.status的计数当c.status =＆＃39;缺席＆＃39;

SELECT    d.empReferenceID,
          Count(c.status) 
FROM      emp_tbl d  
LEFT JOIN empattendance c 
on        d.empReferenceID = c.RefrenceID 
and       c.status='PRESENT' 
and       month(c.CreatedOn)=5 
and       year(c.CreatedOn)=2017 
where     c.RefrenceID not in ('2075671') 
GROUP BY  d.empReferenceID;

Answer 1

不要在WHERE子句中的外连接表上放置条件。你的fortran解散所有外连接记录并将连接转换为内连接。

也许您正在寻找条件聚合，您可以在其中计算不同的状态并在同一结果行中显示计数：

where c.RefrenceID not in ('2075671')

顺便说一句，SELECT d.empReferenceID, Count(c.status) AS count_all, Sum(c.status = 'PRESENT') AS count_present, Sum(c.status = 'Absent') AS count_absent FROM emp_tbl d LEFT JOIN empattendance c ON d.empReferenceID = c.RefrenceID AND month(c.CreatedOn)=5 AND year(c.CreatedOn)=2017 WHERE d.empReferenceID not in ('2075671') GROUP BY d.empReferenceID;行使用了MySQL SUM / true = 1。您可以使用标准SQL实现相同的目标：false = 0或Sum(CASE WHEN c.status = 'PRESENT' THEN 1 ELSE 0 END)。

如何在连接两个表时选择特定值的计数

1 个答案: