Question

I have the following 2 tables:

create table1
(
   SENDER int,
   RECEIVER int,
   TIME time,
   TYPE char(1)
);

create table2
(
   ID int,
   Y int,
   CONTACT int,
   DATE time
);

I am executing the following join query:

SELECT B.ID, A.RECEIVER AS Z, A.SENDER AS CONTACT, A.TYPE, A.TIME
FROM table1 A 
JOIN table2 B ON A.RECEIVER = B.CONTACT 
WHERE A.TYPE = 'A'
   AND A.TIME < B.DATE

How do I modify the query to return only the top 40 results for each (ID,CONTACT) pair using GROUP BY?

I can order the data using the field table2.DATE

Answer 1

since i wanted top 40 results for each ID, i made ID,autoId as a primary key, here autoId is an autoincrement key. so after executing the following query:
SELECT B.ID, A.RECEIVER AS Z, A.SENDER AS CONTACT, A.TYPE, A.TIME
FROM table1 A
JOIN table2 B ON A.RECEIVER = B.CONTACT
WHERE A.TYPE = 'A'
AND A.TIME < B.DATE
i get results such that, the autoId initializes to 1 for each ID
for eg:

ID CONTACT autoId
1    2      1
1    3      2
1    11    3
1    34    4
2    5      1
2    33    2
2    56    3

since autoId is autoincrement, there is already an index on it. after this table is created, i can easily delete the results where autoId is greater than 40. and this while process runs really fast!