Re: [SQL] [SQL, regex, words] how to match word boundaries using regex's?

> I want to do a regex match limited to words.
>
> I tried this:
>
> where ... ~ '\Wword\W';
> where ... ~ '\W*word\W*';
> where ... ~ '\b\(word\)\b';
>
> and other things with LIKE but no joy.

Based on the comments in the source, regexp stuff used in postgres is something like this: http://tiger8.com/us/regexp-manpage.html

I guess there are no backslash macros is POSIX expressions. No joy. By the way, I am wondering what determined the choice of the regexp machine for postgres? Is it performance-related? Is it possible to have the same stuff as in perl?

As to your question, how about a poor man's Altavista like this:

Split the text into words before loading into a special index table. Words are numbered sequentially, so you can search for "phrases":

Table = word
+----------------------------------+----------------------------------+-------+
| Field | Type | Length|
+----------------------------------+----------------------------------+-------+
| rec | char() | 12 |
| seq | int4 | 4 |
| word | text | var |
+----------------------------------+----------------------------------+-------+

SELECT DISTINCT w1.rec
FROM word w1, word w2
WHERE
w1.word ~ '^a$'
AND w2.word ~ '^phrase$'
AND w1.rec = w2.rec
AND w2.seq - w1.seq = 1; -- Distance between the words

This way, you can control what represents the concept of a 'word' by an external program (perl script, etc.)

Certainly, this method will show suboptimal performance with extra large tables and more than three or four words in a seach phrase. But it is possible to optimise by delegating set operations (joins) and position arithmetic to the client. It works very well for my ~500k tables and the most common queries.

--Gene