Checking if a map or array is empty in Presto?

Question

How do I check if a map has no keys in Presto? If I have a way to check if an array is empty, I can use the map_keys function to determine if the map is empty.

Answer 1

You can use the cardinality function: https://prestodb.io/docs/current/functions/array.html#cardinality

select cardinality(array[]) = 0;
 _col0
-------
 true
(1 row)

Answer 2

To check array is empty just compare it with = array[]. Example:

presto> select (map_keys(map(array[], array[])) = array[]) as is_empty;

 is_empty
----------
 true
(1 row)

Likewise, to check if a map is empty just compare it with = map(). Example:

presto> select (map(array[], array[]) = map()) as is_empty;

 is_empty
----------
 true
(1 row)