Question

I know there are a lot of questions regarding using max with a group by but I promise this one is trickier. (ok…so it was so easy it was answered in 10 minutes)

Here’s a sample table

|ID|name|     end_time     |
|01|Bob |2012-02-09 3:00:00|
|02|Bob |2012-02-09 3:15:00|
|03|Ted |2012-02-09 3:00:00|
|04|Ted |null              |

What I want is to return the max time grouped by name but exclude names that have a null end_time.

I started with

SELECT * FROM table t,(
   SELECT MAX(end_time), name FROM table
   GROUP BY name
) last_entry
WHERE t.name = last_entry.name
  AND t.end_time = last_entry.end_time

The problem is that this gives me ID 02 and 03 whereas I want it to return only 02.

Answer 1

If I understood your question correctly, you can solve it by excluding names with null end times in any other row:

SELECT MAX(end_time), name
FROM table t
WHERE NOT EXISTS (
    SELECT 1
    FROM table tt
    WHERE end_time is null AND tt.name=t.name
)
GROUP BY name