On 11/12/20 11:12 AM, David G. Johnston wrote: > On Thu, Nov 12, 2020 at 8:59 AM Andrew Dunstan <andrew@dunslane.net > <mailto:andrew@dunslane.net>> wrote: > > > > So if we then say: > > > select x, j->>x from mytable; > > > you want both result columns named x? That seems like a recipe for > serious confusion. I really don't think this proposal has been > properly > thought through. > > > IMO It no worse than today's: > > select count(*), count(*) from (values (1), (2)) vals (v); > count | count > 2 | 2 >
I guess the difference here is that there's an extra level of indirection. So
select x, j->>'x', j->>x from mytable
would have 3 result columns all named x.
I totally missed the variable reference there - only two of those become "x", the variable reference stays un-rewritten and thus results in "?column?", similar to today:
select count(*), count(*) +1 from (values (1), (2)) vals (v);
count | ?column?
2 | 2
The query rewriter would only rewrite these expressions and provide an expression-related explicit alias clause if the expression is a single operator (same as single function today) and the right-hand side of the operator is a constant (meaning the constant is a reasonable representation of every output value that is going to appear in the result column). If the RHS is a variable then there is no good name that is known to cover all output values and thus ?column? (i.e., do not rewrite/provide an alias clause) is an appropriate choice.
My concerns in this area involve stored views and ruleutils, dump/reload by extension. Greenfield, this would have been nice, and worth the minimal complexity given its usefulness in the common case, but is it useful enough to introduce a whole new default naming mechanism and dealing with dump/restore concerns?
