Re: String searching

On Nov 17, 2014, at 12:55 PM, Robert DiFalco wrote:

> SELECT * FROM MyTable WHERE upper(FullName) LIKE upper('%John%');
>
> That said, which would be the best extension module to use? A "gist" index on the uppercased column? Or something else? Thanks!

Performance wise, I think a function index would probably be the best:

CREATE INDEX mytable_lower_fullname_idx ON mytable(lower(fullname));

SELECT * FROM mytable WHERE lower(fullname) LIKE lower('%john%');

The only reason why I use `lower` and not `upper` is that it's easier to look at when dealing with debugging and sample queries.

I'd bench against GIN and GIST, but I think this will work the best.

The reason is that GIN/GIST use language patterns to simplify the index. so they work great on "words"

select plainto_tsquery('doing watching reading programming');
'watch' & 'read' & 'program'

but not so great on "names":

select plainto_tsquery('john doe');
'john' & 'doe'

select plainto_tsquery('jon doe');
'jon' & 'doe

So you'll get a bit more overhead on the match and you won't get a smaller index (which is why they're great for fulltext)

The search execution might turn out to be much faster. If so, i'd love to know. But doing a lower() search on a lower() function index has always been ridiculously fast for me.

This only goes for names though. If you're searching other fields, then another search method might be considerably better.