Question

I have a table x that’s like the one bellow:

id | name | observed_value |
1  | a    | 100            |
2  | b    | 200            |
3  | b    | 300            |
4  | a    | 150            |
5  | c    | 300            |

I want to make a query so that in the result set I have exactly one record for one name:

  (1, a, 100)
  (2, b, 200)
  (5, c, 300)

If there are multiple records corresponding to a name, say ‘a’ in the table above, I just pick up one of them.

In my current implementation, I make a query like this:

select x.* from x , 
(select distinct name, min(observed_value) as minimum_val
from x group by name) x1
where x.name = x1.name and x.observed_value = x1.observed_value;

But I think there may be some better way around, please tell me if you know, thanks in advance.

EDIT

I am using MySQL and my table contains more than the three columns shown here, so it seems to me that the inner query can not fulfill my requirement.

Answer 1

SELECT  t.*
FROM    (
        SELECT  DISTINCT name
        FROM    mytable
        ) q
JOIN    mytable t
ON      t.id =
        (
        SELECT  id
        FROM    mytable ti
        WHERE   ti.name = q.name
        ORDER BY
                ti.name, ti.observed_value, ti.id
        LIMIT 1
        )

Create an index on (name, observed_value, id) for this query to be efficient.