On 21/07/2025 19:30, Tom Lane wrote:
"Matheus Alcantara" <matheusssil...@gmail.com> writes:
You're right — semantically, using QUALIFY is equivalent to wrapping the
query in a subquery and applying a WHERE clause to the result. The main
motivation here is to provide a more ergonomic and readable syntax.
While I understand the hesitation around introducing another keyword
that effectively acts like WHERE at a different stage, I believe QUALIFY
improves clarity in many use cases, by avoiding the boilerplate and
visual noise of nested subqueries making it easier to write and reason
about.
There are concrete reasons not to do this until/unless it becomes
standardized:
* If the syntax is like WHERE, there will be no way to do it without
making QUALIFY a fully-reserved word. That will inevitably break
more than zero applications. It's a lot easier to justify that
sort of breakage if we can say "QUALIFY is reserved according to
SQL:20xx, so don't blame us".
Yes, it will need to be reserved.
* I'm not exactly convinced that the committee would standardize
it just like this. For one thing, QUALIFY is not even the right
part of speech: it's a verb, and thus more fit to be a primary
statement keyword. What you need here is an adverb (I think ...
been a long time since high school English, but my dictionary
says WHERE is an adverb). Maybe they'd be persuaded to do what
the existing implementations did, but I wouldn't be at all surprised
if they choose a different keyword.
I am pretty sure that the keyword will be QUALIFY. There are just too
many existing implementations for the standard to go against them all.
(Also, another rdbms just implemented it that way in their upcoming
product.)
I agree that we should hold back until the standard accepts it, but
having a working patch ready to go seems like a good idea.
--
Vik Fearing
