On 1/6/16 5:41 PM, Tom Lane wrote:
Since the question makes little sense as stated, I'm going to assume
you mean "can a query like SELECT ... WHERE left(foo, 3) = 'bar'
use an index on column foo?"
The answer to that is no, there is no such optimization built into
Postgres. (In principle there could be, but I've not heard enough
requests to make me think we'd ever pursue it.)
BTW, the case where this would be highly valuable is timestamps. Being
able to do something like date_part('month',timestamptz)='Jan' would be
a big, big deal for warehousing.
--
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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