左连接没有给出想要的结果

Question

我有两个数据集

FEES                    PAYMENTS            
CrsCode InstNo  FEE     Regno   CRSCODE Instno  Payment
CA1        -2   100     R1     CA1      -2       100
CA1        -1   200     R1     CA1      -1       200
CA1         1   200     R1     CA1       1       200
CA1         2   300                 

DESIRED OUTPUT                          
REGNO   CRSCODE INSTNO  FEE PAID    DIFF        
R1          CA1  -2   100   100     0       
R1          CA1  -1   200   200     0       
R1          CA1   1   200   200     0       
R1          CA1   2   300   0       300     

OUTPUT I AM GETTING                         
REGNO   CRSCODE INSTNO     FEE     PAID  DIFF       
R1          CA1   -2       100     100   0
R1          CA1   -1       200     200   0      
R1          CA1    1       200     200   0      
null        null   null    300     null  null

我正在使用的查询

select a.Regno,a.crscode,b.fee,a.payment,b.fee-a.payment from Fees as b Left join
Payments as a on a.CrsCode=b.CrsCode and a.InstNo=b.InstNo

请找到SQLFiddle

Answer 1

;WITH regCrs AS 
(
  SELECT regno, crsCode FROM dbo.PAYMENTS
  GROUP BY regno, crsCode
),
f AS 
( 
  SELECT f.crsCode, f.instNo, f.fee, regCrs.regno
  FROM regCrs INNER JOIN dbo.FEES AS f
  ON regCrs.crsCode = f.crsCode
)
SELECT f.regno, f.crsCode, f.instNo, f.fee,
  paid = COALESCE(p.payment, 0),
  DIFF = f.fee - COALESCE(p.payment, 0)
FROM f
LEFT OUTER JOIN dbo.PAYMENTS AS p
ON f.crsCode = p.crsCode
AND f.instNo = p.instNo;

结果：

REGNO  CRSCODE  INSTNO  FEE  PAID  DIFF
=====  =======  ======  ===  ====  ====
r1     CA1      -2      100  100   0
r1     CA1      -1      200  200   0
r1     CA1      1       200  200   0
r1     CA1      2       300  0     300

SQLfiddle