SQL AST: COUNT cannot return null

[hemberger]

Remove nullability from the PositiveIntReturnTypeExtension for the COUNT function case.

If there are no matching rows, COUNT() returns 0. COUNT(NULL) returns 0.

(source: https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html#function_count)

[staabm]

ah interessting. this changed recently, because I had the impression count would lead to null on empty result sets.

testing it again seems this is not the case:

[staabm]

thank you