15.18. Map Functions and Operators

Subscript Operator: []

The [] operator is used to retrieve the value corresponding to a given key from a map:

SELECT name_to_age_map['Bob'] AS bob_age;

element_at(map<K, V>, key) → V: Returns value for given key, or NULL if the key is not contained in the map.

map() → map<unknown, unknown>

Returns an empty map.

SELECT map(); -- {}

map(array<K>, array<V>) → map<K,V>

Returns a map created using the given key/value arrays.

SELECT map(ARRAY[1,3], ARRAY[2,4]); -- {1 -> 2, 3 -> 4}

See also map_agg() and multimap_agg() for creating a map as an aggregation.

map_concat(map1<K, V>, map2<K, V>, ..., mapN<K, V>) → map<K,V>: Returns the union of all the given maps. If a key is found in multiple given maps, that key’s value in the resulting map comes from the last one of those maps.

transform_keys(map<K1, V>, function) → MAP<K2,V>: See transform_keys().

transform_values(map<K, V1>, function) → MAP<K,V2>: See transform_values().