I find your requirements to be poorly demonstrated by your sample data. There are no negative values and only one tie in the the qa column to break with sa. Perhaps you need to offer clearer sample data and your desired output.

I believe this is just a human-language difficulty. I will assume that by "negative" you mean "non-positive" (zero values).

The spaceship operator provides a far simpler technique for implementing multi-condition sorting.

Notice that there are no conditions in my sorting function's body. Arrays on either side of <=> are synchronously compared element-by-element. By casting the qt values as booleans, 0s become false and non-zeros become true. Furthermore when sorting booleans, false comes before true. By sorting $b <=> $a -- this is DESC sorting. Ergo, trues come before falses.

Sort by qt DESC, then sa DESC: (Demo)

usort(
    $array,
    function($a, $b) {
        return [(bool)$b['qt'], $b['sa']] <=> [(bool)$a['qt'], $a['sa']];
    }
);

Same thing from PHP7.4 and higher (Demo)

usort($array, fn($a, $b) => [(bool)$b['qt'], $b['sa']] <=> [(bool)$a['qt'], $a['sa']]);

The spaceship operator provides a far simpler technique for implementing multi-condition sorting.

Notice that there are no conditions in my sorting function's body. Arrays on either side of <=> are synchronously compared element-by-element. By checking if qt is larger than zero and using that boolean value, zeros become false and non-zeros become true. Furthermore when sorting booleans in DESC order, true comes before false.

Sort by qt non-zeros before zeros, then sa DESC: (Demo)

usort(
    $array,
    function($a, $b) {
        return [$b['qt'] > 0, $b['sa']] <=> [$a['qt'] > 0, $a['sa']];
    }
);

Same thing from PHP7.4 and higher (Demo)

usort($array, fn($a, $b) => [$b['qt'] > 0, $b['sa']] <=> [$a['qt'] > 0, $a['sa']]);

I find your requirements to be poorly demonstrated by your sample data. There are no negative values and only one tie in the the qa column to break with sa. Perhaps you need to offer clearer sample data and your desired output.

The spaceship operator provides a far simpler technique for implementing multi-condition sorting.

Notice that there are no conditions in my sorting function's body. Arrays on either side of <=> are synchronously compared element-by-element.

Sort by qt DESC, then sa DESC: (Demo)

usort(
    $array,
    function($a, $b) {
        return [$b['qt'], $b['sa']] <=> [$a['qt'], $a['sa']];
    }
);

Same thing from PHP7.4 and higher (Demo)

usort($array, fn($a, $b) => [$b['qt'], $b['sa']] <=> [$a['qt'], $a['sa']]);

array_multisort() is more verbose and requires more functions, but is more declarative (Demo)

array_multisort(array_column($array, 'qt'), SORT_DESC, array_column($array, 'sa'), SORT_DESC, $array);

I find your requirements to be poorly demonstrated by your sample data. There are no negative values and only one tie in the the qa column to break with sa. Perhaps you need to offer clearer sample data and your desired output.

I believe this is just a human-language difficulty. I will assume that by "negative" you mean "non-positive" (zero values).

The spaceship operator provides a far simpler technique for implementing multi-condition sorting.

Notice that there are no conditions in my sorting function's body. Arrays on either side of <=> are synchronously compared element-by-element. By casting the qt values as booleans, 0s become false and non-zeros become true. Furthermore when sorting booleans, false comes before true. By sorting $b <=> $a -- this is DESC sorting. Ergo, trues come before falses.

Sort by qt DESC, then sa DESC: (Demo)

usort(
    $array,
    function($a, $b) {
        return [(bool)$b['qt'], $b['sa']] <=> [(bool)$a['qt'], $a['sa']];
    }
);

Same thing from PHP7.4 and higher (Demo)

usort($array, fn($a, $b) => [(bool)$b['qt'], $b['sa']] <=> [(bool)$a['qt'], $a['sa']]);