Re: Or selection on index versus union

han.holl@informationslogik.nl writes:

> PS We still have to be careful how to formulate conditions:
>
> where fase in ('1','2')
>
> is ok, and uses the index, but the logically identical:
>
> where position(fase in '12') >= 1
>
> does a sequential scan.

Right, you would need a functional index to fix that.  The query
optimizer, in general, doesn't know what specific functions
do--they're black boxes.  So there would be no way for the optimizer
to figure out that the two expressions mean the same thing.

-Doug