Re: Puzzled by ROW constructor behaviour?
| От | David G. Johnston |
|---|---|
| Тема | Re: Puzzled by ROW constructor behaviour? |
| Дата | |
| Msg-id | CAKFQuwbcZyooFZ_MmHTEtDepwxovT6pcpfy8iZ1Ag4DBCc+BmA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Puzzled by ROW constructor behaviour? (Eagna <eagna@protonmail.com>) |
| Список | pgsql-general |
On Tue, Nov 22, 2022 at 2:11 PM Eagna <eagna@protonmail.com> wrote:
NUMBER 2
> SELECT ROW(1, 2.5, 'this is a test') = (VALUES (1, 2.5, 'this is a test')) AS test2;
My question is that if a ROW constructor works for a VALUES clause in statement NUMBER 2, then why not NUMBER 3?
You've drawn a false equivalence from the similarity of the syntax.
The following also works:
SELECT 1 = (SELECT 1*1);
But I don't think there is any argument that while this works:
INSERT INTO tbl (col) SELECT 1*1;
This doesn't:
INSERT INTO tbl (col) 1;
There is no difference with replacing 1 with a composite type and the SELECT subquery with VALUES instead.
Your "VALUES" is just a scalar subquery expression that, if it indeed produces a single row and column, can be compared to any other scalar value (if it produces more than one row you will get an error - try it).
David J.
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