$f = ($key, $leftList, $rightList) -> {return <|k:$key, v:ListZipAll($leftList, $rightList)|>;};

$a = [
    <|key: 1, subkey: 11, value: "111"|>,
    <|key: 1, subkey: 12, value: "112"|>,
    <|key: 2, subkey: 21, value: "221"|>,
    <|key: 2, subkey: 22, value: "222"|>,
    <|key: 3, subkey: 33, value: "333"|>,
];

$b = [
    <|key: 1, subkey: 11, value: "111"|>,
    <|key: 2, subkey: 22, value: "222"|>,
    <|key: 3, subkey: 33, value: "333"|>,
    <|key: 4, subkey: 44, value: "444"|>,
    <|key: 5, subkey: 55, value: "555"|>,
];

COMBINE AS_TABLE($a) as A
    PRESORT A.key, A.subkey
WITH AS_TABLE($b) as B
ON A.key = B.key
USING $f(TableRow(), TableRow())