SQL Query，Group by打印太多记录

Question

我有两张桌子

Emp_ID   FirstName
------------------------------
1            John
2            Mark
3            Steve

表2：Emp_Transaction

Trans ID    Emp_ID    start_Date  End_date    Paid_status  Total_Hours     Total_Pay
---------------------------------------------------------
1               1     01/07/13    01/14/2013     True       15.00       75.00
2               1     01/15/13    01/21/2013     False      10.00       50.00
3               1     01/21/13    01/27/2013     False      10.00       50.00

4               2     01/07/13    01/14/2013     False      15.00       75.00
5               2     01/15/13    01/21/2013     False      10.00       50.00
6               2     01/21/13    01/27/2013     False      10.00       50.00

7               3     01/07/13    01/14/2013     True       15.00       75.00
8               3     01/15/13    01/21/2013     True       10.00       50.00
9               3     01/21/13    01/27/2013     False      10.00       50.00

结果应该像这样打印（最早的未付日期）

ID  FirstName   start_Date  End_date    Paid_status  Total_Hours     Total_Pay
--------------------------------------------------------------
1             John      01/15/13    01/21/2013   False      10.00       50.00            
2             Mark      01/07/13    01/14/2013   False      15.00       75.00            
3             steve     01/21/13    01/27/2013   False      10.00       50.00

Answer 1

由于您没有提及您正在使用的RDBMS，因此以下查询几乎适用于所有RDBMS（并非所有）

SELECT  a.*, b.*
FROM    users a
        INNER JOIN Emp_transaction b
            ON a.Emp_ID = b.Emp_ID
        INNER JOIN
        (
            SELECT  Emp_ID, MIN(start_DATE) min_date
            FROM    emp_transaction
            WHERE   Paid_Status = 'False'
            GROUP   BY Emp_ID
        ) c ON b.Emp_ID = c.Emp_ID AND
                b.start_date = c.min_DATE

• SQLFiddle Demo

但是如果您的RDBMS支持Window Functions，

SELECT  a.*,
        b.TransID, b.start_Date, b.End_date, 
        b.Paid_status, b.Total_Hours, b.Total_Pay
FROM    users a
        INNER JOIN
        (
            SELECT  TransID, Emp_ID, start_Date, End_date, Paid_status, Total_Hours, Total_Pay,
                    ROW_NUMBER() OVER (PARTITION BY Emp_ID ORDER BY start_Date ASC) rn
            FROM    emp_transaction
            WHERE   Paid_status = 'False'
        ) b ON a.Emp_ID = b.Emp_ID AND
                b.rn = 1

• SQLFiddle Demo