SQL统计部门人数,人数为0的部门也要显示出来

相同点：它们都以一张部门表（或类别表），其它表都有部门编号DepartmentID（类别编号）

案例一：一张表

select c.DepartmentID,c.DepartmentName, t.Num AS '人员数量' from T_Department as c
left join (select DepartmentID,COUNT(*) AS Num from T_User group by DepartmentID) as t on c.DepartmentID= t.DepartmentID

核心思想就是：拆分

1将人员表按部门编号统计数量：（ select DepartmentID,COUNT(*) AS Num from T_User group by CompanyID）得到t：部门编号、部门人员数量；

2将部门表与 t ，根据部门编号联表左连接，得到：部门名称、部门人员数量

案例二：多张表

统计提交的调查人员、设备、规范、数据来源规范表的数量

select c.CompanyID,c.CompanyName, t1.Num AS '调查人员数量',t2.Num AS '设备数量',t.Num AS '规范数量',t3.Num AS '数据来源规范数量' from T_Company as c
left join (select CompanyID,COUNT(*) AS Num from T_Standard as s where s.HasSubmitted=1 group by CompanyID) as t on c.CompanyID= t.CompanyID
left join (select CompanyID,COUNT(*) AS Num from T_Investigator as s where s.HasSubmitted=1 group by CompanyID) as t1 on c.CompanyID= t1.CompanyID
left join (select CompanyID,COUNT(*) AS Num from T_Machine as s where s.HasSubmitted=1 group by CompanyID) as t2 on c.CompanyID= t2.CompanyID
left join (select CompanyID,COUNT(*) AS Num from T_DataSource as s where s.HasSubmitted=1 group by CompanyID) as t3 on c.CompanyID= t3.CompanyID
order by c.CompanyID

最后赋值粘贴到Excel，在Excel搞个合计：

巴特西

SQL统计部门人数,人数为0的部门也要显示出来

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