ydb/yql/essentials/tests/sql/suites/expr/dict_builtins_null_lookup.sql

/* postgres can not */

$d2 = AsDict(AsTuple(1/1, "bar"));
$d3 = AsDict(AsTuple(1/0, "baz"));

$t1 = AsDict(AsTuple(AsTuple(1,   "key"), AsTuple(1,   "value")));
$t2 = AsDict(AsTuple(AsTuple(1/1, "key"), AsTuple(2/1, "value")));
$t3 = AsDict(AsTuple(AsTuple(1/0, "key"), AsTuple(123, "value")));

SELECT
    DictContains($d2, null),  -- false, no such key
    DictContains($d3, null),  -- true, null is convertible to Nothing<T> for any T

    DictLookup($d2, null),    -- Nothing(String?), no such key
    DictLookup($d3, null);    -- Just("baz"), null is convertible to Nothing<T> for any T


SELECT
    DictContains($t1, AsTuple(1, "keyy")),       -- false, missing key
    DictContains($t1, AsTuple(1, "key")),        -- true,  match
    DictContains($t1, Just(AsTuple(1, "key"))),  -- true,  match with optional

    DictContains($t2, AsTuple(null, "key")),   -- false, no such key
    DictContains($t3, AsTuple(null, "key")),   -- true, null is convertible to Nothing<T> for any T

    DictLookup($t2, AsTuple(null, "key")),     -- Nothing(Tuple<Int32?, String>?), no such key
    DictLookup($t3, AsTuple(null, "key"));     -- Just(AsTuple(123, "value")), null is convertible to Nothing<T> for any T