> 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).
