Using Regular Expressions to Parse SQL

[ct60 at aol.com]

Firstly, thanks to those who posted.

I just do not understand how the non-greedy operator works.

Using the following code:

import re

s = "qry_Lookup.desc = CSS_Rpt1.desc AND qry_Lookup.lcdu1 =
CSS_Rpt1.lcdu"

pat = "(.+=)+?(.+)"

m = re.match(pat, s)

if m is None:
    print "No Match"
else:
    for mat in m.groups():
        print mat

I would expect that the first group would match one or more times with
the fewest amount of text.  However the result is:

>qry_Lookup.desc = CSS_Rpt1.desc AND qry_Lookup.lcdu1 =
> CSS_Rpt1.lcdu

The first match of the "=" char is still greedy.  I would have
expected:
qry_Lookup.desc =
> CSS_Rpt1.desc AND qry_Lookup.lcdu1
> =
> CSS_Rpt1.lcdu

I'm obviously missing something because the non-greedy match seems to
not be acting as expected.

Any insights would be greatly appreciated.

Thanks in advance,

Chris (ct60 at aol.com)



On Feb 5, 9:31 am, c... at aol.com wrote:
> Hello again -
>
> I do not seem to be able to get a handle on non-greedy pattern
> matching.
>
> I am trying to parse the following - note that there are no line
> breaks in the string:
>
> " FROM ((qry_Scores_Lookup1 INNER JOIN CSS_Rpt1 ON
> (qry_Scores_Lookup1.desc = CSS_Rpt1.desc) AND
> (qry_Scores_Lookup1.lastcdu = CSS_Rpt1.lastcdu))"
>
> What I would like to do is be able to split on the "AND" and the "="
> to come up with the following:
> qry_Scores_Lookup1.desc
> CSS_Rpt1.desc
> qry_Scores_Lookup1.lastcdu
> CSS_Rpt1.lastcdu
>
> The following is one of my many attempts to do this:
>
> import re
>
> s= " FROM ((qry_Scores_Lookup1 INNER JOIN CSS_Rpt1 ON
> (qry_Scores_Lookup1.desc = CSS_Rpt1.desc) AND
> (qry_Scores_Lookup1.lastcdu = CSS_Rpt1.lastcdu))"
>
> pat = " FROM .+ (?:INNER|LEFT|RIGHT) JOIN .+ ON (?:AND)*?((.+)=(.+))"
>
> m = re.match(pat, s)
>
> if m is None:
>     print "No Match"
> else:
>     for mat in m.groups():
>         print mat
>
> My pattern does not even come close.
>
> Any help would be greatly appreciated.  My goal is to analyse a large
> number of SQL querys to try to identify the join field and see where
> indexing might make sense.
>
> While I am mostly interested in understanding regular expressions, I
> would also be interested in knowing about any Python SQL parsers out
> there.
>
> Thanks in advance.
>
> Chris (c... at aol.com)