Re: Querying date_time for date only ?

Aarni Ruuhim�ki wrote:
> Hello List,
> 
> I have a time stamp without time zone field, YYYY-MM-DD hh:mm:ss, in
> my table.  I want to also find something just for a particular day
> regardless of the time.
> 
> (Pg)SQL way to do this ?

Yes.  You can use date_trunc():
test=> select date_trunc('day', '2004-01-04 04:02:03'::timestamp);     date_trunc--------------------- 2004-01-04
00:00:00(1row)
 

so it would be date_trunc('day', col) = '2004-01-05'.  The problem with
this is that you cannot use an index unless you create an expression
index on the date_trunc() function call.  Another option is to do
something like:
WHERE col >= '2004-01-04' AND col < '2004-01-05'

If the date isn't a constant, you have to use date_trunc() on those, and
add one day to the second comparison:
  WHERE col >= date_trunc('day', col2) AND     col < date_trunc('day', col2) + '1 day';

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