Question

Database:

Transaction  ProductID
 1              1000
 2              1000
 2              1001 
 3              1000
 3              1002
 4              1000
 4              1001
 5              1003

and L1 table (i keep Frequenties item)

PRODUCTID  SUPPORT
  1000       4
  1001       2
  1002       1
  1003       1

According to L1 table, how to find this result with a T-SQL statement? And find support value from my Transaction table?

+-------------+-----------+-----------------+
| PRODUCTID1  | PRODUCTID2|     SUPPORT     |
+-------------+-----------+-----------------+
|      1000   |   1001    |         2       |
+-------------+-----------+-----------------+
|      1000   |   1002    |         1       |
+-------------+-----------+-----------------+
|      1000   |   1003    |         0       |
+-------------+-----------+-----------------+
|      1001   |   1002    |         0       |
+-------------+-----------+-----------------+
|      1001   |   1003    |         0       |
+-------------+-----------+-----------------+
|      1002   |   1003    |         0       |,
+-------------+-----------+-----------------+

Test Table:

create table transactions(
   ORDERID    INT,
   PRODUCTID INT
);

insert into transactions(ORDERID, PRODUCTID)
values ('1', '1000')
      ,('2', '1000')
      ,('2', '1001')
      ,('3', '1000')
      ,('3', '1002')
      ,('4', '1000')
      ,('4', '1001'),
       ('5', '1003');

  CREATE TABLE L1
(PRODUCTID INT,
SUPPORT INT )

 INSERT INTO L1 (PRODUCTID,SUPPORT)
   SELECT PRODUCTID,COUNT(*) [SUPPORT] FROM transactions
                    GROUP BY PRODUCTID                        
                    ORDER BY PRODUCTID

Thanks in advance.

Answer 1

WITH Pairs 
     As (SELECT A.PRODUCTID AS PRODUCTID1, 
                B.PRODUCTID AS PRODUCTID2 
         FROM   L1 A 
                JOIN L1 B 
                  ON A.PRODUCTID < B.PRODUCTID) 
SELECT PRODUCTID1, 
       PRODUCTID2, 
       COUNT(t2.ORDERID) AS SUPPORT
FROM   Pairs 
       LEFT JOIN transactions t1 
         ON t1.PRODUCTID = PRODUCTID1 
       LEFT JOIN transactions t2 
         ON t2.PRODUCTID = PRODUCTID2 
            AND t1.ORDERID = t2.ORDERID 
GROUP  BY PRODUCTID1, 
          PRODUCTID2