TRANSFORM_KEYS

SinceVersion dev

Description

Applies a lambda expression to every entry in a map and constructs a new map with the transformed keys and the original values. The lambda receives the key and value of each entry.

Syntax

TRANSFORM_KEYS((<key>, <value>) -> <new_key>, <map>)

Parameters

Parameter	Description
<key>	The lambda parameter representing the key of a map entry.
<value>	The lambda parameter representing the value of a map entry.
<new_key>	An expression that produces the key in the returned map. Its type must be supported by MAP keys.
<map>	A MAP<K, V> expression.

Return Value

Returns a MAP<K2, V>, where K2 is the type returned by the lambda.

• The values in the input map are retained unchanged.
• If <map> is empty, returns an empty map.
• If <map> is NULL, returns NULL.
• A NULL key returned by the lambda is retained.
• If multiple entries are transformed to the same key, the value from the last occurrence is retained.

Examples

SELECT transform_keys((k, v) -> k + 10, map(1, 10, 2, 20)) AS result;

+----------------+
| result         |
+----------------+
| {11:10, 12:20} |
+----------------+

SELECT transform_keys((k, v) -> 1, map(1, 10, 2, 20)) AS result;

+--------+
| result |
+--------+
| {1:20} |
+--------+

SELECT transform_keys((k, v) -> k, CAST(NULL AS MAP<INT, INT>)) AS result;

+--------+
| result |
+--------+
| NULL   |
+--------+