$structVariantType = Variant<a: Int32, b: String>;

$optionalVariantData = [
    <|variantValue: Just(Variant(1,       "a", $structVariantType))|>,
    <|variantValue: Nothing(OptionalType($structVariantType))|>,
    <|variantValue: Just(Variant("hello", "b", $structVariantType))|>,
];

SELECT variantValue.a AS aAlternative, variantValue.b AS bAlternative FROM as_table($optionalVariantData);