Re: TEXT vs VARCHAR join qual push down diffrence, bug or expected?

On Wed, Sep 23, 2015 at 7:29 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Removing that entirely would be quite incorrect, because then you'd be
> lying to the parent node about what collation your node outputs.
>

Yes. I too thought so and thus wanted to fix that code block by
considering the default collation.

>
> After thinking a bit more about the existing special case for non-foreign
> Vars, I wonder if what we should do is change these code blocks to look
> like
>
> collation = r->resultcollid;
> if (collation == InvalidOid)
> state = FDW_COLLATE_NONE;
> else if (inner_cxt.state == FDW_COLLATE_SAFE &&
> collation == inner_cxt.collation)
> state = FDW_COLLATE_SAFE;
> + else if (collation == DEFAULT_COLLATION_OID)
> + state = FDW_COLLATE_NONE;
> else
> state = FDW_COLLATE_UNSAFE;
>
> That is, only explicit introduction of a non-default collation causes
> a subexpression to get labeled FDW_COLLATE_UNSAFE. Default collations
> would lose out when getting merged with a nondefault collation from a
> foreign Var, so they should work all right.
>

Agree.
I had suggested similar changes in approach (2)
but you put that check at exact required place.

> regards, tom lane
>

--
Jeevan B Chalke
Principal Software Engineer, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company