Re: substring and POSIX re's

Tom Lane wrote:

>Don Isgitt <djisgitt@soundenergy.com> writes:
>
>
>>gds2=# select substring('NE NE SE 2310 FSL 330 FEL' from '^([A-Z][A-Z] )+');
>> substring
>>-----------
>> SE
>>(1 row)
>>
>>
>
>
>
>>The pg docs say that this form of substring uses POSIX re's, and my
>>understanding of POSIX re's is they are always greedy. So, why do I get
>>only SE instead of NE NE SE? Pilot error, probably, but would someone
>>please enlighten me? Thank you very much.
>>
>>
>
>I think you want
>
>regression=# select substring('NE NE SE 2310 FSL 330 FEL' from '^(([A-Z][A-Z] )+)');
> substring
>-----------
> NE NE SE
>(1 row)
>
>ie, you need the "+" to be *inside* the capturing parentheses.  When
>it's outside, I guess the engine chooses to consider the last match
>of the parenthesized subexpression as the thing to return.  (I can't
>recall if this choice is specified in the docs or not.)
>
>            regards, tom lane
>
>
>
>

Thanks, Tom. Interestingly enough, neither my original query or your
corrected one returns anything with pg 7.4--another good reason to
upgrade to 8.*

Don