Greg Stark <stark@mit.edu> writes:
> On 19 Sep 2014 19:40, "Josh Berkus" <josh@agliodbs.com> wrote:
>> Yeah, here's an example of the canonical case:
>>
>> Table t1 ( a, b, c )
>>
>> - "b" is low-cardinality
>> - "c" is high-cardinality
>> - There are separate indexes on both b and c.
>>
>> SELECT a, b, c FROM t1
>> WHERE b = 2
>> ORDER BY c LIMIT 1;
> You badly want a partial index on c WHERE b=2 for each value of 2 which
> appears in your queries.
Well, if it's *only* b = 2 that you ever search for, then maybe a partial
index would be a good answer. Personally I'd use a plain btree index on
(b, c). The planner's been able to match this type of query to
multicolumn indexes for a long time.
regards, tom lane