返回两个最近日期的记录之间的差异的SQL查询

我有下表：

**TABLE1**

RecordID    UserID      UserName       Balance     TranDate
---------------------------------------------------------------
100         10001       John Doe       10213.00    2013-02-12 00:00:00.000
101         10001       John Doe        1932.00    2013-04-30 00:00:00.000
102         10001       John Doe       10213.00    2013-03-25 00:00:00.000
103         10001       John Doe       14514.00    2013-04-12 00:00:00.000
104         10001       John Doe        5430.00    2013-02-19 00:00:00.000
105         10001       John Doe       21242.00    2010-02-11 00:00:00.000
106         10001       John Doe       13342.00    2013-05-22 00:00:00.000

现在我要做的是查询最近的两个事务，并得出以下数据：

RecordID    UserID      UserName       Balance     TranDate
---------------------------------------------------------------
106         10001       John Doe       13342.00    2013-05-22 00:00:00.000
101         10001       John Doe        1932.00    2013-04-30 00:00:00.000

然后，使用上述数据，我想比较余额以显示差异：

UserID      UserName       Difference 
---------------------------------------------------------------
10001       John Doe       -11410.00

这只是显示了前两个余额（最新余额和最新余额之前的余额）之间的差异

现在我有下面的问题。这样可以显示最近的两个事务

SELECT  
 TOP 2  *
  FROM  Table1
 WHERE  UserID  = '1001'
 ORDER
    BY  TranDate DESC

现在我的问题是：

上面的sql是否可以安全使用？我只是依靠ORDER by DESC关键字对TranDate进行排序，我不确定这是否非常可靠

如何选择两个余额之间的差额（第2行-第1行）？我在网上寻找一些答案，我找到了一些关于自我加入的东西。我试过了，但它没有显示我想要的输出

编辑：

这是我能得到的最接近我想要的结果。有人能帮我一下吗？谢谢

DECLARE @SampleTable TABLE
(
 UserID       INT,  
 UserName     VARCHAR(20),   
 Balance      DECIMAL(9,2) DEFAULT 0
)

INSERT 
  INTO  @SampleTable
       (UserID, UserName, Balance)
SELECT  
 TOP 2  UserID,
        UserName,
        Balance
  FROM  Table1
 WHERE  UserID  = '1001'
 ORDER
    BY  TranDate DESC


 SELECT  A.UserID,
         A.UserName,
         B.Balance - A.Balance AS Difference
   FROM  @SampleTable A
   JOIN  @SampleTable B
     ON  A.UserID  = B.UserID    

---

非常感谢

假设SQL Server作为RDBMS，您应该能够使用如下内容：

;with cte as
(
  select recordid, userid, username, balance, trandate,
    row_number() over(partition by userid order by trandate desc) rn
  from table1 
) 
select c1.userid, c1.username,
  c1.balance - c2.balance diff
from cte c1
cross apply cte c2
where c1.rn = 1
  and c2.rn = 2;

看

或者，也可以使用行\编号值上的内部联接来完成此操作：

;with cte as
(
  select recordid, userid, username, balance, trandate,
    row_number() over(partition by userid order by trandate desc) rn
  from table1 
) 
select c1.userid, c1.username,
  c1.balance - c2.balance diff
from cte c1
inner join cte c2
  on c1.rn + 1 = c2.rn
where c1.rn = 1

---

请参见

假设SQL Server作为RDBMS，您应该能够使用如下内容：

;with cte as
(
  select recordid, userid, username, balance, trandate,
    row_number() over(partition by userid order by trandate desc) rn
  from table1 
) 
select c1.userid, c1.username,
  c1.balance - c2.balance diff
from cte c1
cross apply cte c2
where c1.rn = 1
  and c2.rn = 2;

看

或者，也可以使用行\编号值上的内部联接来完成此操作：

;with cte as
(
  select recordid, userid, username, balance, trandate,
    row_number() over(partition by userid order by trandate desc) rn
  from table1 
) 
select c1.userid, c1.username,
  c1.balance - c2.balance diff
from cte c1
inner join cte c2
  on c1.rn + 1 = c2.rn
where c1.rn = 1

---

见

谢谢！这正是我需要的！我只是做了一些调整，缩小了结果范围，效果很好！谢谢这正是我需要的！我只是做了一些调整，缩小了结果范围，效果很好！