Re: WHERE clause with timestamp data type

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Chirag Patel <patelc75(at)yahoo(dot)com> writes:
> The following command works great,
> SELECT AVG(column) FROM table WHERE timestamp > 2007-08-23;

No it doesn't.  It might not actively fail, but it isn't selecting the
rows you think it is.  You want this:

SELECT AVG(column) FROM table WHERE timestamp > '2007-08-23';

Comparing EXPLAIN outputs reveals what's really going on:

regression=# create table tab (col float, ts timestamp);
CREATE TABLE
regression=# explain SELECT AVG(col) FROM tab WHERE ts > 2007-08-23;
                         QUERY PLAN                         
------------------------------------------------------------
 Aggregate  (cost=35.81..35.82 rows=1 width=8)
   ->  Seq Scan on tab  (cost=0.00..34.45 rows=543 width=8)
         Filter: ((ts)::text > '1976'::text)
(3 rows)

regression=# explain SELECT AVG(col) FROM tab WHERE ts > '2007-08-23';
                                QUERY PLAN                                 
---------------------------------------------------------------------------
 Aggregate  (cost=31.73..31.75 rows=1 width=8)
   ->  Seq Scan on tab  (cost=0.00..30.38 rows=543 width=8)
         Filter: (ts > '2007-08-23 00:00:00'::timestamp without time zone)
(3 rows)

[ For the archives: this is another example of why implicit casts to
text are evil ... PG 8.3 will reject the first query above, instead
of imputing a surprising meaning to it. ]

			regards, tom lane