Re: COALESCE requires NULL from scalar subquery has a type

Rowan Collins <rowan.collins@xxxxxxxxx> · Tue, 9 Feb 2016 16:58:02 +0000



    David G. Johnston wrote on 08/02/2016
      16:05:

    
      On Mon, Feb 8, 2016 at
          8:25 AM, Geoff Winkless <pgsqladmin@xxxxxxxx> wrote:

      
          On 8 February 2016 at 14:49, Tom Lane <tgl@xxxxxxxxxxxxx>
              wrote:

              > Yup.  The output column type of the sub-SELECT is
              determined without

              > reference to its context, so there's nothing causing
              the unknown-type

              > literal to get assigned a definite type.

              
            Mm. I can follow that, although it makes me unhappy
            that casting the

            literal to a known type fixes this, it seems unintuitive.

          
            While
              explicit casting of literals can at times be annoying and
              seemingly unncessary I wouldn't call it unintuitive.
          
        
    I think if I was designing Postgres's type system (or SQL itself?)
    from scratch, I'd try to make literals look less like strings. I
    think part of what's unintuitive is that we're so used to thinking
    of 'Yes' as representing a text value, when Postgres doesn't see it
    that way. Perhaps if it was "Select text<yes>", and even
    "Select int<42>" it would be more obvious that "Select
    <yes>" or "Select <42>" required type inference.

    
    But that's just dreaming...

    
    Regards,

    -- 

    Rowan Collins

    [IMSoP]