Re: Using ANY()

On Sun, 2009-06-07 at 19:33 +0100, Shakil Shaikh wrote:
> Hi all,
>
> Is it appropriate to use ANY() in a select statement as so?
>
> SELECT * FROM table t WHERE t.id = ANY(ARRAY[1,2,3]);

Yes, that's appropriate. A simpler formulation (for that simple case)
is:

    ... WHERE t.id IN (1,2,3)

> A less trivial usage of the above would be to pass an array to a simple
> function using it to return a range of arbitrary rows.

I don't know exactly what you mean by that.

>  The alternative to
> this would be to (programmatically) call the function multiple times on a
> list of arguments. Some questions:

Generally you don't want to submit multiple queries to answer one
question.

> 1) How does ANY() behave on indexed columns?

It can use an index.

> 2) How does ANY() behave when passed an array with one element?

The same as when passed multiple elements. The planner treats it
differently than just doing "t.id = 1", but it can still use an index.
It appears more likely to use a bitmap index scan plan, and maybe it
can't use a normal index scan in that situation.

> 3) Generally is it better to use ANY on a passed ARRAY, or to just call a
> select multiple times (and aggregate the results)? Is ANY just a glorified
> OR?

Using ANY or IN is generally better. The planner is able to do the index
scan in one pass using ANY or IN; if you use a chain of ORs it does
multiple bitmap scans and ORs the results together.

You should try experimenting a little to find the answers to questions
like this. EXPLAIN and EXPLAIN ANALYZE can tell you a lot.

Regards,
    Jeff Davis