$input = SELECT * FROM AS_TABLE([
    <|k: 1, v: 1|>,
    <|k: 2, v: 2|>,
    <|k: 3, v: 3|>,
    <|k: 4, v: 4|>,
    <|k: 5, v: 5|>,
]);

SELECT (SELECT 3) AS x;

SELECT (SELECT Avg(v) FROM $input) AS x;

SELECT (SELECT Avg(v) FROM $input WHERE v == 3) AS x;