如何从一个表中选择多个不同的数据？

Question

Following is my table and I want to select the records having unique id1 and minimum difference, I have already tried this:

select * from table group by (id1) having min(difference)

but this returns only one record

| ID1 | ID2 | DIFFERENCE |
|-----|-----|------------|
|   1 |   1 |          1 |
|   1 |   2 |          3 |
|   1 |   3 |          4 |
|   2 |   1 |          3 |
|   2 |   3 |          4 |

Now I want to select the records having minimum difference ie I want first row and 4th row from table because both having minimum difference and different id1.

Answer 1

Try using sub-query like this:

SELECT DISTINCT t1.* FROM Table1 t1
JOIN
(
    SELECT ID1, MIN(difference) AS MinDif
    FROM Table1
    GROUP BY ID1
) t2
ON t1.ID1 = t2.ID1
AND t1.difference = t2.MinDif;

If you want to select only ID1 and Difference columns then you can do this even without using sub-query:

SELECT ID1, MIN(difference) AS MinDif
FROM Table1
GROUP BY ID1

See this SQLFiddle