基于三列联接两个表

Question

For MS-Access, how do I accomplish following. I was thinking of writing VBA loop but I think it will take a while.

Here are the two tables:

Table A

 |  id  |   Day  | Month |  F_value1 
 --------------------------------------- 
 |  1   |   10   |   11  |  523 
 |  1   |   11   |   11  |  955 
 |  2   |   1    |   11  |  45
 |  2   |   2    |   11  |  49

Table B

 |  id  |   Day  | Month |  G_value1 
 --------------------------------------- 
 |  1   |   10   |   11  |  19923 
 |  1   |   11   |   11  |  55455 
 |  2   |   1    |   11  |  45454

What I need:

 |  id  |   Day  | Month |  F_value1 | G_value1
 ----------------------------------------------- 
 |  1   |   10   |   11  |  523      | 19923    
 |  1   |   11   |   11  |  955      | 55455 
 |  2   |   1    |   11  |  45       | 45454
 |  2   |   2    |   11  |  49       | Null

I tried Access Query designer but I had no luck. I'm not sure how to go about it in SQL. I already have table setup.

For programming way, I'm thinking

for each row in Table A
 for each row in Table B
   If TableA.fields = TableB.fields 
   Then Insert it into new table
 End loop
End loop

Answer 1

You need multiple conditions for the join s. Fortunately, MS Access supports this with LEFT JOIN :

SELECT a.id, a.Day, a.Month, a.F_value1, b.G_Value1
FROM TableA as a LEFT JOIN
     TableB as b
     ON a.ID = b.ID AND a.day = b.day AND a.month = b.month;

You can use INSERT to insert into an existing table; INTO to create a new table. Or just run the query to get the results.

Answer 2

In SQL View, this should work and ideally be quicker than your suggested loop

SELECT a.*, b.G_Value1
INTO TableC
FROM TableA a
LEFT JOIN TableB b
ON a.ID=b.ID

Answer 3

If you need full join (ie all records of A and all records of B:

SELECT A.ID, A.Day, A.Month, A.F_value1, B.G_value1
FROM A LEFT JOIN B ON (A.Month= B.Month) AND (A.Day= B.Day) AND (A.ID = B.ID)
UNION
SELECT B.ID, B.Day, B.Month, A.F_value1, B.G_value1
FROM B LEFT JOIN A ON (B.ID = A.ID) AND (B.Day= A.Day) AND (B.Month= A.Month);