Обсуждение: Where is using a table name as a "row value" documented?
Hi,
I asked this on Stackoverflow[0] months ago, and finally posting it here as well, along with Laurenz Albe's helpful comments:
The query `SELECT * FROM table WHERE NOT (table IS NOT NULL);` finds all the rows in `table` that have a `null` value in any column. This answer[1] helped understand the logic of it, but wanted to understand this syntax. Another answer[2] states that "the reference to the table (alias) refers to an existing row" and the[PostgreSQL `SELECT` documentation's `WHERE` section[3] states that "a row satisfies the condition if it returns true when the actual **row values** are substituted for any variable references" (emphasis mine). A keyword search on "row values"[4] yielded references to the 4.2 Value Expressions[5] page, but I couldn't find an answer there either (unless I overlooked something).
> the technical term in PostgreSQL is a "whole-row reference",
> and it doesn't seem to be documented except in the source
> code. By using the table name as a column, you get a composite
> value consisting of all columns.
>
> You can see
>
> SELECT tab FROM tab;
>
> as being the same as
>
> SELECT ROW(tab.*) FROM tab;
[0]: https://stackoverflow.com/questions/77191458/where-is-using-a-table-name-as-a-row-value-documented
[1]: https://stackoverflow.com/a/31035052/1498178
[2]: https://stackoverflow.com/a/69087309/1498178
[3]: https://www.postgresql.org/docs/current/sql-select.html#SQL-WHERE
[4]: https://www.postgresql.org/search/?q=row%20value
[5]: https://www.postgresql.org/docs/current/sql-expressions.html
> You can see
>
> SELECT tab FROM tab;
>
> as being the same as
>
> SELECT ROW(tab.*) FROM tab;
>
> This is non-standard behavior (as is the use of * inside
> a ROW() constructor).
Unfortunately, neither the row constructor docs[7] nor the pages referenced there mention this usage anywhere (unless I missed it somehow). I also found this answer[8] helpful when trying to find the relevant docs.
Appreciatively,
Attila
[0]: https://stackoverflow.com/questions/77191458/where-is-using-a-table-name-as-a-row-value-documented
[1]: https://stackoverflow.com/a/31035052/1498178
[2]: https://stackoverflow.com/a/69087309/1498178
[3]: https://www.postgresql.org/docs/current/sql-select.html#SQL-WHERE
[4]: https://www.postgresql.org/search/?q=row%20value
[5]: https://www.postgresql.org/docs/current/sql-expressions.html
On Friday, December 8, 2023, Gulyás Attila <toraritte@gmail.com> wrote:
Unfortunately, neither the row constructor docs[7] nor the pages referenced there mention this usage anywhere (unless I missed it somehow). I also found this answer[8] helpful when trying to find the relevant docs.
I found this fairly,quickly when looking for what can be used as a column reference. But I agree that this might need to be documented elsewhere as well.
David J.