如何联接两个SQL语句

Question

我有两个查询，它们返回正确的结果。 其中之一是：

select distinct epr.DepartmentCode 
from [dbo].[EmployeePayRates] epr 
join [dbo].[EmployeeTimecards] et on epr.EmployeeID = et.EmployeeID 
where StoreID = 89

它检查曾经在商店89中签入过的所有不同部门的员工。查询返回：

DepartmentCode
1
2
5

第二个查询是：

SELECT DISTINCT 
    DepartmentCode, count(DISTINCT EmployeeID) 
FROM [dbo].[EmployeeTimecards] 
WHERE EmployeeTimecardDate = '2013-11-25' 
  AND StoreID = 89 
GROUP BY 
   DepartmentCode

它返回今天在商店89中每个部门的雇员人数。表如下所示：

DepartmentCode          EmployeeCount
1                       17
5                       7

我正在尝试使其看起来像：

DepartmentCode          EmployeeCount
1                       17
2                       0
5                       7

如果有人向我展示如何加入这些查询，我将不胜感激。 提前致谢。

Answer 1

您可以将第一个查询移动到子查询中，然后将LEFT JOIN返回到表中，并执行相同的计数：

WITH DepartmentCodes AS
(   SELECT  DISTINCT epr.DepartmentCode 
    FROM    [dbo].[EmployeePayRates] epr 
            JOIN [dbo].[EmployeeTimecards] et 
                ON epr.EmployeeID = et.EmployeeID 
    WHERE   StoreID = 89
)
SELECT  dc.DepartmentCode,
        EmployeeCount = COUNT(DISTINCT c.EmployeeID)
FROM    DepartmentCodes dc
        LEFT JOIN [dbo].[EmployeeTimecards]  c
            ON dc.DepartmentCode = c.DepartmentCode
            AND EmployeeTimecardDate = '20131125' 
            AND StoreID = 89 
GROUP BY dc.DepartmentCode;

yyyyMMdd我将您的字符串文字日期更改为区域性不变格式yyyyMMdd因为在某些地区甚至ISO标准yyyy-MM-dd都可能被误解为yyyy-dd-MM 。 尽管不是本文的重点，但Aaron Bertrand在其错误处理日期/范围查询的文章中涵盖了此格式问题

Answer 2

我选择使用Common Table表达式来连接两个查询。 在我的博客（ http://craftydba.com/?p=1234）上查看我的CTE文章。

--
-- Join cteDeptCode 2 cteEmpPerDept
--
;
with cteDeptCode (DeptCode) as
(
select distinct epr.DepartmentCode 
from [dbo].[EmployeePayRates] epr 
join [dbo].[EmployeeTimecards] et 
on epr.EmployeeID = et.EmployeeID 
where StoreID = 89
),
cteEmpPerDept(DeptCode, EmpCnt) as
(
SELECT DISTINCT 
DepartmentCode, count(DISTINCT EmployeeID) 
FROM [dbo].[EmployeeTimecards] 
WHERE 
EmployeeTimecardDate = '2013-11-25' AND StoreID = 89 
GROUP BY DepartmentCode
)
select d.DeptCode, a.EmpCnt 
from cteDeptCode d 
left join cteEmpPerDept e 
on d.DeptCode = e.DeptCode