Question

I have a table like below:

COL1  | COL2   | COL3
______________________
ITEM1 | CLASS1 | DATE1
ITEM2 | CLASS3 | DATE2
ITEM3 | CLASS1 | DATE3
ITEM4 | CLASS2 | DATE4
ITEM5 | CLASS1 | DATE2
ITEM6 | CLASS3 | DATE6
ITEM7 | CLASS2 | DATE3
.
.

I want to arrange the data by descending date and then get the top 2 entries for every class. I am unable to figure out how to do this. Please help.

Answer 1

Try this query, it ranks records in a group, then uses rank to filter result –

SELECT col1, col2, col3 FROM (
  SELECT e1.*, COUNT(*) p FROM entries e1
    LEFT JOIN entries e2
      ON e1.col2 = e2.col2 AND e1.col3 <= e2.col3
    GROUP BY e1.col2, e1.col3
  ) t
WHERE p < 3

+-------+--------+-------+
| col1  | col2   | col3  |
+-------+--------+-------+
| ITEM5 | CLASS1 | DATE2 |
| ITEM3 | CLASS1 | DATE3 |
| ITEM7 | CLASS2 | DATE3 |
| ITEM4 | CLASS2 | DATE4 |
| ITEM2 | CLASS3 | DATE2 |
| ITEM6 | CLASS3 | DATE6 |
+-------+--------+-------+