presto cardinality map

prestoのcardinalityはmapのsizeを返す。mapは↓のような構造。

presto> select cardinality(map(ARRAY[1,2,3,4,5],ARRAY[3,4,4,5,6]));
 _col0
-------
     5
(1 row)
presto> select map(ARRAY[1,2,3,4,5],ARRAY[3,4,4,5,6]);
           _col0
---------------------------
 {1=3, 2=4, 3=4, 4=5, 5=6}
(1 row)

https://prestodb.io/docs/current/functions/map.html