On Sun, Jul 16, 2023 at 8:48 PM PG Doc comments form <nore...@postgresql.org> wrote: > > The following documentation comment has been logged on the website: > > Page: https://www.postgresql.org/docs/15/queries-with.html > Description: > > Hi. > > In the queries WITH documentation > https://www.postgresql.org/docs/15/queries-with.html it is a bit confusing > that MERGE is referenced in several places as being something you can use > inside with, even though it can't. > > If you search for MERGE on the page, you will find the 2 first results is a > reference saying MERGE can be used inside WITH, the same as SELECT, INSERT, > UPDATE, or DELETE. The 3rd result then correctly states that MERGE cannot be > used inside WITH. > > If I'm misunderstanding the meaning of the first 2 results, then I apologise > :) > > Greetings > Rasmus Porsager
I agree. The second one is kind of confusing. > WITH w AS ( > SELECT key, very_expensive_function(val) as f FROM some_table > ) > SELECT * FROM w AS w1 JOIN w AS w2 ON w1.f = w2.f; > Here, materialization of the WITH query ensures that very_expensive_function > is evaluated only once per table row, not twice. > The examples above only show WITH being used with SELECT, but it can be > attached in the same way to INSERT, UPDATE, DELETE, > or MERGE. There are two "SELECT". " only show WITH being used with SELECT", not mention of "SELECT" refer to the auxiliary statements or primary statements. -- I recommend David Deutsch's <<The Beginning of Infinity>> Jian
