Re: Regex query not using index

On Feb 19, 2008, at 9:32 PM, Postgres User wrote:

> I'm running a simple query on 8.2. With this syntax, Explain indicate
> that the index is scanned:
> select * from eod where name = 'AA'
>
> However, when I change the query to use simple regex:
> select * from eod where name ~ 'AA'
>
> now Explain indicates a seq scan:
> Index Scan using equity_eod_symbol_idx on equity_eod (cost=0.00..8.27
> rows=1 width=149)
> Index Cond: ((symbol)::text = 'AA'::text)
>
> Is there any way to 'encourage' Postgres to hit the index when using
> regex? Do I need to create a functional index or something?
> Without the index in play, I really can't use regex on any of my
> larger tables.

You need it to be anchored:

select * from eod where name ~ '^AA';

If you're looking to be able to use indexes for searches within a
string then, for 8.2, you'll need to check out tsearch2.

Erik Jones

DBA | Emma®
erik(at)myemma(dot)com
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