Using Regular expressions on a Database?

[Anon]

Hi everyone,
I'm kinda new at this so just bear with me...
Has anyone come across a way to evaluate a regular expression directly to a database?

What I have in mind is just a control on a webpage where the user types in their regular expression which would then be evaluated against the DB - writing the results to a dynamic page.

Is this possible? Any info would be a great help. If it's not possible I'd like to hear that too.

Thanks,
Rob.

[Anon]

Regexs are not in the sql standard, so the exact method is database-dependent. E.g. in mysql you write WHERE column REGEXP 'pattern' whereas PostgreSQL requires WHERE column ~ 'pattern'.

[smarlowe]

Note that postgresql now also supports POSIX regular expressions as well as the LIKE simple pattern matching. Issuing 'man 7 regex' on most Gnu boxes will give you a nice simple three page man page on the syntax, which is dirt easy, but fairly powerful.

They are invoked by using just a ~, ~, !~, and ~! for case sensitive match, case insensitive match, case sensitive NOT match, and case insensitive NOT match respectively.

No like keywork is used.

Interestingly, you SHOULD be able to build an index on them with the functions built in. I'll give it a try some day and see if it works.

[Anon]

Just a quick thank you for passing on your ideas, just being pointed on in the right direction is great - although if you find out anythng else, I'd be more than happy to hear what you all have to say. (o:

Thanks again and enjoy he rest (what's left)of the weekend.
Rob.

[smarlowe]

Note that indexing on a function in any dbms with a regex may result in exponential growth of indexes if you have even just a few nested regexes. This is because an index on a function has to produce all the possible outputs ahead of time and store them, and with a complex enough regex, there may be a huge number of possible outputs.