Re: Index on multiple columns VS multiple index

Hi Brice,

On Jan 2, 2014, at 2:24 PM, Brice André wrote:

> Yes, except that on b, it's a inequality operator.
>
>
> 2014/1/2 Jonathan S. Katz <jonathan(dot)katz(at)excoventures(dot)com>
> On Jan 2, 2014, at 2:17 PM, Brice André wrote:
>
>> Hello everyone,
>>
>> I have a question concerning index : suppose I have a table with fields 'a' and 'b' and that all requests perform WHERE clauses on 'a' field, and some requests also perform WHERE clauses on 'b' fields. What is the best approach for indexing strategy:
>> One index on 'a' and one on 'b'
>> One index on both columns 'a' and 'b'
>> A combination of both solutions ?
>
> Could you clarify your question a bit? Are you saying your queries are predominantly
>
> SELECT ... FROM table WHERE a = ?
>
> With some queries that are
>
> SELECT ... FROM table WHERE a = ? AND b = ?
>
> Thanks,
>
> Jonathan

Moving your reply to the list.

Assuming the data type you are using supports B-tree indexes, I can't think of any cases where inequality (specifically <> or !=) would use an index, so a single index on 'a' is what you are looking for.

However, if you are doing anything with equality (<, <=, =, >=, >) then you would wnat a multi-column index on (a,b), in that column order.

Best,

Jonathan