Re: Incomplete or misleading explanation of the data types for mathematical operators

On Thu, Mar 5, 2020 at 08:03:19PM -0700, Sergei Agalakov wrote:
> On 3/5/2020 7:29 PM, Bruce Momjian wrote:
> > On Wed, Jan 29, 2020 at 07:35:18PM +0000, PG Doc comments form wrote:
> > > Multiplication preserves data type, exponentiation silently converts bigint
> > > to double, but preserves numeric data type, square root silently converts
> > > both int and numeric types to double.
> > > The best would be to explain this behaivior of operators like it was done
> > > for mathematical functions.
> > Uh, how does this relate to bitwise operators? Why would we mention
> > type changes for things like exponentiation in the bitwise operator
> > documentation section?
> >
> This chapter is named "Mathematical Functions and Operators". The table 9.4.
> is named "Mathematical Operators". I don't see on this page any section
> "Bitwise operators" so I don't really understand your complaint.
> How do you understand the phrase "The bitwise operators work only on
> integral data types, whereas the others are available for all numeric data
> types. "  in the context of the table "Mathematical Operators"?
> I understand it that all other mathematical operators except bitwise
> operators do exist for all numeric data type.
> In what place by your opinion documentation should describe that some
> mathematical operators exist only for some numeric data types but not
> others?
> I have given examples of such operators - exponentiation and square root
> aren't defined for all numeric data types and do hidden conversion of the
> data types.

Ah, I see what you are saying now --- there are operators listed above
that are not supported by all numeric data types, so "the others are
available for all numeric data types" is false. I think the text was
written because non-integer calls to bit-wise functions _fail_, rather
than being silently converted:

SELECT 1::float4 | 1;
ERROR: operator does not exist: real | integer
LINE 1: SELECT 1::float4 | 1;
^
HINT: No operator matches the given name and argument types. You might
need to add explicit type casts.

but I see your point. I guess we could change the word "available" to
"silently converted", but it seems best to just remove that phrase.
Documentation patch attached.

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Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

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