【ClickHouse】How to create index for Map Type Column or one key of it?

How to create index for Map Type Column or one key of it?
[version 21.8.10 revision 54449] #31801

You can create index for map keys, or for map values. Example:

CREATE TABLE test_table
(
    id UInt64,
    value Map(Int64, String),
    index value_key_index mapKeys(value) TYPE bloom_filter GRANULARITY 4
) ENGINE=MergeTree ORDER BY id;

Link to documentation https://clickhouse.com/docs/en/engines/table-engines/mergetree-family/mergetree/#available-types-of-indices.

Reference resources ：https://github.com/ClickHouse/ClickHouse/issues/31801