>> For that to return zero, it would also be necessary for "SELECT 2+2" >> to return zero rows. Which would be consistent with some views of the >> universe, but not particularly useful.
> Given that:
> SELECT *; > Results in: > SQL Error: ERROR: SELECT * with no tables specified is not valid
That has nothing to do with the number of rows, though. That's complaining that there are no columns for the * to refer to.
Interesting to note that SELECT * FROM table_with_zero_cols does not complain of anything.
postgres=# select * from test1; -- (0 rows)
This I believe result of the fact that we allow user to drop all columns of a table.
On a side note, Postgres allows me to do this (which I don't think is a bug or useless): I inserted some rows into a table, and then dropped the columns. The resulting table has no columns, but live rows.
postgres=# select * from test_0_col_table ; -- (200000 rows)
> I get that the horse has already left the barn on this one but neither "0" > nor "1" seem particularly sound answers to the question "SELECT count(*)".
Yeah, it's more about convenience than principle. AFAICS there are three defensible answers to what an omitted FROM clause ought to mean:
1. It's not legal (the SQL spec's answer). 2. It implicitly means a table of no columns and 1 row (PG's answer). 3. It implicitly means a table of no columns and 0 rows (which is what I take Gurjeet to be advocating for).
I wasn't advocating it, but was trying to wrap my head around why Postgres would do something like count(*) of nothing == 1.