in reply to Re^4: Documentation of REGEXP support in DBD::SQLite?
in thread Documentation of REGEXP support in DBD::SQLite?

> It shouldn't matter for complicated the regular expressions are,

Sorry that's bordering at nonsense hubris.

To take advantage of the index you need to identify character sequences in the regex.° (And erix even showed that it only works for 3+ characters in PG.)

Now, while it's possible to identify those sequences at the compile phase - at least in Perl using re - one need's to know which ones are

And regexes are Turing complete.

It might be possible with sufficient work involved, but I doubt it's already done.

You are more than welcome to prove me wrong. Even with a test/benchmark in PG.

Claiming that the complexity doesn't matter is really quite a bold statement.

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

°) if they even appear in the regex!

  • Comment on Re^5: Documentation of REGEXP support in DBD::SQLite?

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Re^6: Documentation of REGEXP support in DBD::SQLite?
by LanX (Saint) on Nov 21, 2024 at 14:34 UTC
    OK, my first concept was that substrings in the regex are identified and the rows filtered in a first step before applying the regexe to them. Kind of Danny's idea.

    But ... If the regex is decomposed to a query with simpler sub rexes and the Boolean logic is delegated to the SQL engine building a plan....

    Well I have to admit, this could be very efficient for complex regexes

    I tried to look into the PQ documentation, unfortunately it doesn't give much insight, except that substrings with at least 3 characters are needed.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    see Wikisyntax for the Monastery

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