Re: Confusing reference to MERGE use inside WITH
On Sun, Jul 16, 2023 at 5:48 AM PG Doc comments form 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. No, they are not, see below. The 3rd result then correctly states that MERGE cannot be > used inside WITH. > > Yes. The first non-intro section says that the following syntax is allowed (you can attach WITH /TO/ MERGE) [ WITH with_query [, ...] ] MERGE INTO [ ONLY ] target_table_name [ * ] [ [ AS ] target_alias ] https://www.postgresql.org/docs/current/sql-merge.html The second section is saying that the "with_query" above cannot contain MERGE, i.e., you cannot put MERGE /IN/ WITH Namely because you cannot attach a RETURNING clause to MERGE. The intro makes it quite clear as well: Specifically, reading the last sentence makes it clear: Each auxiliary statement in a WITH clause can be a SELECT, INSERT, UPDATE, or DELETE; and the WITH clause itself is attached to a primary statement that can be a SELECT, INSERT, UPDATE, DELETE, or MERGE. Here the inside is called the auxiliary while the outside is called primary. David J.
Re: Confusing reference to MERGE use inside WITH
On Sun, Jul 16, 2023 at 8:48 PM PG Doc comments form 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 <> Jian
Improvement of clarity in pg_ctl command docummentation
The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/15/app-pg-ctl.html Description: I was reading the documentation about pg_ctl and there everything was well written about the usage and option that can be used with the pg_ctl command but there is not mentioned that we can not run pg_ctl command as root and why we cant run it as root.
Confusing reference to MERGE use inside WITH
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
