sql - Ignore results that generate an error -

i'm trying make following request

select login, time table    time::timestamp <= (current_timestamp - interval '5' month); 

where time text field containing timestamps.

is there way can ignore ignore rows generate cast error when time not formatted ?

i've tried following

select login, time table    (((current_timestamp - interval '6' month)::text || time)::timestamp     <= (current_timestamp - interval '5' month); 

but first, in not beautiful , second, results in error: time zone displacement out of range error, don't understand.

you can write own cast function in plpgsql error handling.

 create or replace function to_timestamp_ignore_errors(text) returns timestamp $$ begin   return $1::timestamp; exception when others   return null; end; $$ language plpgsql immutable strict;  postgres=# select to_timestamp_ignore_errors('bbbb');  to_timestamp_ignore_errors  ----------------------------  (1 row)  postgres=# select to_timestamp_ignore_errors('2013-08-16');  to_timestamp_ignore_errors  ----------------------------  2013-08-16 00:00:00 (1 row) 

other possibility format check before casting - initial version

 create or replace function to_timestamp_ignore_errors(text) returns timestamp $$ -- regular should richer  select case when $1 ~ '^\d{4}-\d{2}-\d{2}$' $1::timestamp else null end; $$ language sql;        create function postgres=# select to_timestamp_ignore_errors('2013-08-16');  to_timestamp_ignore_errors  ----------------------------  2013-08-16 00:00:00 (1 row)  postgres=# select to_timestamp_ignore_errors('bbbb');  to_timestamp_ignore_errors  ----------------------------  (1 row) 

tested on 9.2

regular expression based version should little bit faster (30%) when there minimum errors, , faster when lot of errors, solution preferable. so, preferable solution cleaning data , using types.