Re: Selecting the most recent timestamptz

[Ken Tanzer <ken.tanzer@xxxxxxxxx>]

On Thu, Feb 22, 2018 at 1:09 AM, Alexander Farber <alexander.farber@xxxxxxxxx> wrote:

Good morning, there are these 2 records in a table:

# select m.played, m.mid, m.action, m.gid, m.uid from words_moves m where gid=10;
            played             | mid | action | gid | uid
-------------------------------+-----+--------+-----+-----
 2018-02-19 14:42:08.46222+01  |  12 | play   |  10 |   9
 2018-02-20 15:06:01.430634+01 | 216 | expire |  10 |  11
(2 rows)

I try to get the record with the latest timestamp by adding a NOT EXISTS condition -

# select m.played, m.mid, m.action, m.gid, m.uid from words_moves m where gid=10 and not exists (select 1 from words_moves x where m.mid=x.mid AND x.played > m.played);
            played             | mid | action | gid | uid
-------------------------------+-----+--------+-----+-----
 2018-02-19 14:42:08.46222+01  |  12 | play   |  10 |   9
 2018-02-20 15:06:01.430634+01 | 216 | expire |  10 |  11
(2 rows)

Why are still 2 records returned? I am probably overlooking something simple, sorry...

Thank you

Alex

In your example, you have different values for mid.  I'm thinking you meant gid?

select m.played, m.mid, m.action, m.gid, m.uid from words_moves m where gid=10 and not exists (select 1 from words_moves x where m.gid=x.gid AND x.played > m.played);

On a related note for the list, I know of at least two other ways to do this.  Are any of them better and worse?

SELECT DISTINCT ON (gid) [fields] FROM words_moves m WHERE gid=10 ORDER BY gid,played DESC

SELECT [fields] FROM words_moves m WHERE gid=10 ORDER BY played DESC limit 1;

Cheers,

Ken

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