Обсуждение: greedy or not? regexps...
Hi, I am trying to understand the function substring. Here: select SUBSTRING(cit1.summary, '=([0-9]*)') from cms_items cit1 where cit1.summary ~* '.*linkadministration.*[0-9]*'; gives me two empty strings and select SUBSTRING(cit1.summary, '=([0-9]{1,10})') from cms_items cit1 where cit1.summary ~* '.*linkadministration.*[0-9]*'; gives me the right values. However, bizarrely, select SUBSTRING(ban1.url_id, '=([0-9]*)') from banner ban1 where ban1.url_id ~* '.*linkadministration.*[0-9]*'; select SUBSTRING(ban1.url_id, '=([0-9]{1,10})') from banner ban1 where ban1.url_id ~* '.*linkadministration.*[0-9]*'; Both give me the same result!!! The difference being that in case two the numbers I am catching are at the end of the strings and in case 1 in the middle. Is this normal? Which is correct? Cheers Anton
"Anton Melser" <melser.anton@gmail.com> writes: > I am trying to understand the function substring. You haven't actually said anything that sounded surprising; and in any case, without seeing the data being operated on, we can't comment much on what's happening. I will note that '=([0-9]*)' is going to match to the *first* "=" in the string, whether there happen to be any digits after it or not, because the *-construct can match zero characters. regards, tom lane
Intellectually challenged Anton strikes again! I wanted +, not *. Sometimes I think I'm not cut out for IT! :-( Thanks heaps, Anton On 23/02/07, Tom Lane <tgl@sss.pgh.pa.us> wrote: > "Anton Melser" <melser.anton@gmail.com> writes: > > I am trying to understand the function substring. > > You haven't actually said anything that sounded surprising; and in any > case, without seeing the data being operated on, we can't comment much > on what's happening. I will note that '=([0-9]*)' is going to match > to the *first* "=" in the string, whether there happen to be any digits > after it or not, because the *-construct can match zero characters. > > regards, tom lane >