Thread: WHERE clause with timestamp data type

WHERE clause with timestamp data type

From

Chirag Patel

Date:

27 August 2007, 04:49:38

The following command works great,
SELECT AVG(column) FROM table WHERE timestamp > 2007-08-23;

But when I try it with finer resolution (hour, minutes, seconds) like this, I get a syntax error
SELECT AVG(heartrate) FROM heartrates WHERE timestamp > 2007-08-23 19:48:09;

Do I need to convert from string format to total number of seconds? Any ideas on how to get this work?

Thanks!
Chirag

Re: WHERE clause with timestamp data type

From

Tom Lane

Date:

27 August 2007, 05:14:13

Chirag Patel <patelc75@yahoo.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

Re: WHERE clause with timestamp data type

From

"A. Kretschmer"

Date:

27 August 2007, 05:24:31

am  Sun, dem 26.08.2007, um 21:49:29 -0700 mailte Chirag Patel folgendes:
> The following command works great,
> SELECT AVG(column) FROM table WHERE timestamp > 2007-08-23;
>
> But when I try it with finer resolution (hour, minutes, seconds) like this, I
> get a syntax error
> SELECT AVG(heartrate) FROM heartrates WHERE timestamp > 2007-08-23 19:48:09;

Can you show us the error?


>
> Do I need to convert from string format to total number of seconds? Any ideas
> on how to get this work?

Try: "WHERE timestamp > '2007-08-23 19:48:09'::timestamp ";


Btw.: bad idea to title a column 'timestamp', because this is a
datatype-identifier - but it works.


Andreas
--
Andreas Kretschmer
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