Question

Need help with Min Function in SQL

I have a table as shown below.

+------------+-------+-------+
|   Date_    | Name  | Score |
+------------+-------+-------+
| 2012/07/05 | Jack  |     1 |
| 2012/07/05 | Jones |     1 |
| 2012/07/06 | Jill  |     2 |
| 2012/07/06 | James |     3 |
| 2012/07/07 | Hugo  |     1 |
| 2012/07/07 | Jack  |     1 |
| 2012/07/07 | Jim   |     2 |
+------------+-------+-------+

I would like to get the output like below

+------------+------+-------+
|   Date_    | Name | Score |
+------------+------+-------+
| 2012/07/05 | Jack |     1 |
| 2012/07/06 | Jill |     2 |
| 2012/07/07 | Hugo |     1 |
+------------+------+-------+

When I use the MIN() function with just the date and Score column I get the lowest score for each date, which is what I want. I don’t care which row is returned if there is a tie in the score for the same date. Trouble starts when I also want name column in the output. I tried a few variation of SQL (i.e min with correlated sub query) but I have no luck getting the output as shown above. Can anyone help please:)

Query is as follows

SELECT DISTINCT 
A.USername, A.Date_, A.Score 
FROM TestTable AS A 
INNER JOIN (SELECT Date_,MIN(Score) AS MinScore 
FROM TestTable 
GROUP BY Date_) AS B 
ON (A.Score = B.MinScore) AND (A.Date_ = B.Date_);

Answer 1

Use this solution:

SELECT a.date_, MIN(name) AS name, a.score
FROM tbl a
INNER JOIN
(
    SELECT date_, MIN(score) AS minscore
    FROM tbl
    GROUP BY date_
) b ON a.date_ = b.date_ AND a.score = b.minscore
GROUP BY a.date_, a.score

SQL-Fiddle Demo

This will get the minimum score per date in the INNER JOIN subselect, which we use to join to the main table. Once we join the subselect, we will only have dates with names having the minimum score (with ties being displayed).

Since we only want one name per date, we then group by date and score, selecting whichever name: MIN(name).

If we want to display the name column, we must use an aggregate function on name to facilitate the GROUP BY on date and score columns, or else it will not work (We could also use MAX() on that column as well).