Обсуждение: select extract and subqueries

> I don't know if its possiable or not but I've been having problems
> trying to extract the timestamp out of one of my columns so that I can
> compare the dates.
...
> but if I try to use a subquery to get the date it gives me a parse
> error.
> en=# SELECT EXTRACT (EPOCH FROM TIMESTAMP (select date from master));
> ERROR:  parser: parse error at or near "select"
> is this simply just a limitation of the extract funtion or am I
> missing something?

I'm not *certain* I can tell from your example what you actually want to
do. However, if you want to compare two timestamps (or timestamp vs
date) to see if they are from the same day, then you can use
date_trunc(), like so:

  select date_trunc('day', date) from master;

Presumably your query will end up looking something like:

  select * from master where date_trunc('day', date) = date 'today';

hth

                     - Thomas