Laurenz Albe <laurenz.albe@xxxxxxxxxxx> writes: > I found this in a blog (https://buttondown.email/jaffray/archive/sql-scoping-is-surprisingly-subtle-and-semantic/): > CREATE TABLE aa (a INT); > INSERT INTO aa VALUES (1), (2), (3); > CREATE TABLE xx (x INT); > INSERT INTO xx VALUES (10), (20), (30); > SELECT (SELECT sum(a) FROM xx LIMIT 1) FROM aa; > sum > ═════ > 6 > (1 row) > Huh? Shouldn't that return three rows, just like No. The aggregate function is semantically of the closest query level that contributes a Var to its argument, so it's evaluated at the "FROM aa" level, causing that level to become an aggregated query that returns just one row. Then it acts like an outer reference as far as the sub-select is concerned. This is documented at the end of Section 4.2.7 in our manual, https://www.postgresql.org/docs/current/sql-expressions.html#SYNTAX-AGGREGATES Thank the SQL spec for that weirdness. regards, tom lane
