使用 SQL Server 查询从考勤日志表和员工表中获取空值？

Question

我有这样的查询来提取数据：

SELECT 
    e.EmpName,
    d.DepartmentName,
    l.EnrollNumber,
    v.VerifyModeName,
    CAST(PunchTime as DATE)Check_Date,MIN(CAST(PunchTime as Time))[TimeIN], MAX(Cast(PunchTime as Time))[TimeOUT],
        RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 3600 AS VARCHAR),2) + ':' +
        RIGHT('0' + CAST((DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 60) % 60 AS VARCHAR),2)  + ':' +
        RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) % 60 AS VARCHAR),2) as Duration
FROM 
    Department d, 
    VerifyModes v, 
    Employee e 
FULL OUTER JOIN AttLog l 
    ON e.EnrollNumber=l.EnrollNumber
WHERE
    e.DeptID = d.Id
    AND l.VerifyMode = v.VerifyModeId 
GROUP BY 
    e.EmpName, d.DepartmentName, l.EnrollNumber, v.VerifyModeName, CAST(PunchTime as DATE)
ORDER BY Check_Date

结果是这样的：

虽然我已经包含了full outer join 条件。

如果我只使用：

select e.EmpName, l.PunchTime 
from Employee e 
full outer join AttLog l 
    on e.EnrollNumber = l.EnrollNumber

结果显示Employee 和NULL PunchTime：

那么，如何修复上述查询以获得包含NULL PunchTime 的结果？

然后，当我添加日期条件时，查询仍然没有再次显示 NULL 。如何纠正？

SELECT 
            e.EmpName,
            d.DepartmentName,
            l.EnrollNumber,
            v.VerifyModeName,
            CAST(PunchTime as DATE)Check_Date,MIN(CAST(PunchTime as Time))[TimeIN], MAX(Cast(PunchTime as Time))[TimeOUT],
                RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 3600 AS VARCHAR),2) + ':' +
                RIGHT('0' + CAST((DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 60) % 60 AS VARCHAR),2)  + ':' +
                RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) % 60 AS VARCHAR),2) as Duration
        FROM Department d    
        INNER JOIN Employee e
            ON e.DeptID = d.Id
        LEFT JOIN AttLog l 
            ON e.EnrollNumber = l.EnrollNumber
        LEFT JOIN VerifyModes v
            ON l.VerifyMode = v.VerifyModeId 
        WHERE cast(l.PunchTime as Date) between '2015-07-22' and '2015-07-22'
        GROUP BY 
            e.EmpName, d.DepartmentName, l.EnrollNumber, v.VerifyModeName, CAST(PunchTime as DATE)

        ORDER BY Check_Date

Answer 1

尝试改用LEFT JOIN：

SELECT 
    e.EmpName,
    d.DepartmentName,
    l.EnrollNumber,
    v.VerifyModeName,
    CAST(PunchTime as DATE)Check_Date,MIN(CAST(PunchTime as Time))[TimeIN], MAX(Cast(PunchTime as Time))[TimeOUT],
        RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 3600 AS VARCHAR),2) + ':' +
        RIGHT('0' + CAST((DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) / 60) % 60 AS VARCHAR),2)  + ':' +
        RIGHT('0' + CAST(DATEDIFF(SECOND, MIN(CAST(PunchTime as Time)), MAX(Cast(PunchTime as Time))) % 60 AS VARCHAR),2) as Duration
FROM Department d    
INNER JOIN Employee e
    ON e.DeptID = d.Id
LEFT JOIN AttLog l 
    ON e.EnrollNumber = l.EnrollNumber
LEFT JOIN VerifyModes
    ON l.VerifyMode = v.VerifyModeId 
GROUP BY 
    e.EmpName, d.DepartmentName, l.EnrollNumber, v.VerifyModeName, CAST(PunchTime as DATE)
ORDER BY Check_Date

---

注意：Avoid using old-style JOIN syntax.

---

编辑： 不要将日期比较放在WHERE 子句中，而是将其放在JOIN 条件中：

LEFT JOIN Attlog l
    ON e.DeptID = d.Id
    AND cast(l.PunchTime as Date) between '2015-07-22' and '2015-07-22'

将比较放在WHERE 子句中会将查询转换为INNER JOIN，从而删除NULL 行。