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transform_keys

Description

Transforms keys in a map using a Lambda expression and produces a new key for each entry in the map.

This function is supported from v3.0.

From v2.5, StarRocks supports querying complex data types MAP and STRUCT from data lakes. MAP is an unordered collection of key-value pairs, for example, {"a":1, "b":2}.

You can use external catalogs provided by StarRocks to query MAP and STRUCT data from Apache Hive™, Apache Hudi, and Apache Iceberg. You can only query data from ORC and Parquet files. For more information about how to use external catalogs to query external data sources, see Overview of catalogs and topics related to the required catalog type.

Syntax

MAP transform_keys(lambda_func, any_map)

lambda_func can also be placed after any_map:

MAP transform_keys(any_map, lambda_func)

Parameters

  • any_map: the Map.

  • lambda_func: the Lambda expression you want to apply to any_map.

Return value

Returns a map value where the data types of keys are determined by the result of the Lambda expression and the data types of values are the same as values in any_map.

If any input parameter is NULL, NULL is returned.

If a key or value in the original map is NULL, NULL is processed as a normal value.

The Lambda expression must have two parameters. The first parameter represents the key. The second parameter represents the value.

Examples

The following example uses map_from_arrays to generate a map value {1:"ab",3:"cdd",2:null,null:"abc"}. Then the Lambda expression is applied to each key to increment the key by 1.

mysql> select transform_keys((k,v)->(k+1), col_map) from (select map_from_arrays([1,3,null,2,null],['ab','cdd',null,null,'abc']) as col_map)A;
+------------------------------------------+
| transform_keys((k, v) -> k + 1, col_map) |
+------------------------------------------+
| {2:"ab",4:"cdd",3:null,null:"abc"}       |
+------------------------------------------+