On 1/6/16 5:15 PM, Seamus Abshere wrote:
I've been using Postgres for years ( :heart: ) and I'm still in doubt
about this. Would somebody provide an authoritative, definitive,
narrative answer?
-> Can a function like `LEFT()` use an index?
(Or do I have to find an "equivalent" operator in order to leverage
indexes?)
If you're looking for magic here, there is none.
CREATE INDEX ON a(field);
... WHERE field = LEFT(...) -- can use index
... WHERE LEFT(field) = ... -- can NOT use index
CREATE INDEX ON a(LEFT(field,5))
... WHERE field = LEFT(...) -- can NOT use index
... WHERE LEFT(field,5) = ... -- CAN use index
... WHERE LEFT(field,6) = ... -- can NOT use index
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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