Question

我需要SELECT查询的帮助，我需要在其中加入另一个表并获取最大日期记录。我已经创建了示例来演示。我的最后一个SELECT是不正确的，我需要指导来修复它，或者在Sql server 2014中有更好的方法

CREATE TABLE #EmpTable
(
    EmpNum INT,
    colA VARCHAR(5) NULL,
    colB VARCHAR(5) NULL
)

CREATE TABLE #EmpDetailTbl
(
    EmpNum INT,
    Name VARCHAR(10),
    Department VARCHAR(10) NULL,
    ReportDate DATETIME NOT NULL
)

INSERT INTO #EmpTable 
VALUES (101, 'val11', 'Val21'), (102, 'val12', 'Val21'), (103, 'val13', 'Val23');

INSERT INTO #EmpDetailTbl 
VALUES (101, 'emp101', 'Dept1', '05/01/2018'), (101, 'emp101', 'Dept2', '06/01/2018'),
       (101, 'emp101', 'Dept1', '05/01/2017'), (102, 'emp102', 'Dept3', '04/01/2018'),
       (102, 'emp102', 'Dept1', '05/01/2018')

--select * from  #EmpDetailTbl
--select * from  #EmpTable

SELECT 
    a.EmpNum, Name, ColA, ColB, Department
FROM 
    #EmpTable a
LEFT OUTER JOIN
    #EmpDetailTbl b ON a.EmpNum = b.EmpNum 
                    AND ReportDate = (SELECT MAX(ReportDate) 
                                      FROM #EmpDetailTbl 
                                      a.EmpNum = b.EmpNum)

Answer 1

使用rank()分析函数根据报告日期枚举行，然后仅为每位员工选择第一行：

SELECT EmpNum, Name, ColA, ColB, Department
FROM (
  SELECT 
    a.EmpNum, b.Name, a.ColA, a.ColB, b.Department,
    rank() over (partition by a.EmpNum order by b.ReportDate desc) as rn
  FROM #EmpTable a
  LEFT JOIN #EmpDetailTbl b ON 
    a.EmpNum = b.EmpNum
  ) t
WHERE rn = 1;

此查询将处理关系：如果员工的记录超过1条且具有相同日期且也恰好是最大值，则会全部显示。

Answer 2

如果我理解正确，你可以试试这个以获得MaxDate行。

使用exists按MAX(b1.ReportDate)

获取EmpNum

select a.EmpNum, Name, ColA, ColB, Department
FROM #EmpTable a
LEFT JOIN #EmpDetailTbl b on a.EmpNum = b.EmpNum 
WHERE exists (
    SELECT 1
    FROM #EmpDetailTbl b1
    WHERE b1.EmpNum = b.EmpNum
    GROUP BY b1.EmpNum
    HAVING MAX(b1.ReportDate) = b.ReportDate
)

sqlfiddle：https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=a3deade95dbd25d9cadadee37e16d9c6

<强>结果

EmpNum  Name    ColA    ColB    Department
101    emp101   val11   Val21   Dept2
102    emp102   val12   Val21   Dept1
103    emp103   val13   Val23   Dept1

Answer 3

ReportDate应该是a.ReportDate

从具有最大日期的另一个表中选择数据

3 个答案: