Re: Array index not used for query on first element?

Tom Lane wrote:

>> It seemed reasonable to me that a select on the first element of an
>> array column could use an index on the column, but, as seen in this
>> example, I can't get it to do so:
>
> Nope. The operators that go along with a btree index are equality,
> less than, etc on the whole indexed column. btree knows nothing
> about extracting array elements.

I guess I was working by analogy with queries like this:

select * from someTable where textColumn like 'foo%';

This will happily use an ordinary btree index on textColumn, right?
(Although I know it's only for the C locale with the default op
class.) Anyway, I guess this is a far more common case than matching
the prefix of an array. Like another poster suggested, I can have an
additional expression index on the first element of my array column.

- John Burger
MITRE