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Operations on Maps

A MAP type can be created using the syntax MAP<type, type>. For example MAP<VARCHAR, INT> is a map from strings to integers.

In CREATE TABLE and CREATE TYPE declarations there is no way to specify the nullability of the values of a MAP. The compiler will always assume that map keys are not nullable, while values elements are nullable:

CREATE TABLE T(m MAP<VARCHAR, INT>);

Table T will have a single column m whose values are nullable maps, the map's keys are non-nullable VARCHAR values, while the maps's values are nullable INT values.

Map literals​

Map literals have the syntax MAP[key , value ( , key , value )* ]. Here is an example: SELECT MAP['hi',2].

Predefined functions on map values​

FunctionDescriptionExample
map[key]Returns the element in the map with the specified key. If there is no such key, the result is NULL.MAP['x', 4, 'y', 3]['x'] => 4
CARDINALITY(map)Returns the number of key-value pairs in the map.CARDINALITY(MAP['x', 4]) => 1