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Version: Latest-3.2

map_size

Description​

Returns the number of elements in a MAP value. MAP is an unordered collection of key-value pairs, for example, {"a":1, "b":2}. One key-value pair constitutes one element, for example, {"a":1, "b":2} contains two elements.

This function has an alias cardinality(). It is supported from v2.5.

Syntax​

INT map_size(any_map)

Parameters​

any_map: the MAP value from which you want to retrieve the number of elements.

Return value​

Returns a value of the INT type.

If the input is NULL, NULL is returned.

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

Examples​

Query MAP data from a StarRocks native table​

From v3.1 onwards, StarRocks supports defining MAP columns when you create a table. This example uses table test_map, which contains the following data:

CREATE TABLE test_map(
    col_int INT,
    col_map MAP<VARCHAR(50),INT>
  )
DUPLICATE KEY(col_int);

INSERT INTO test_map VALUES
(1,map{"a":1,"b":2}),
(2,map{"c":3}),
(3,map{"d":4,"e":5});

SELECT * FROM test_map ORDER BY col_int;
+---------+---------------+
| col_int | col_map       |
+---------+---------------+
|       1 | {"a":1,"b":2} |
|       2 | {"c":3}       |
|       3 | {"d":4,"e":5} |
+---------+---------------+
3 rows in set (0.05 sec)

Obtain the number of elements in each row of the col_map column.

select map_size(col_map) from test_map order by col_int;
+-------------------+
| map_size(col_map) |
+-------------------+
|                 2 |
|                 1 |
|                 2 |
+-------------------+
3 rows in set (0.05 sec)

Query MAP data from data lake​

This example uses Hive table hive_map, which contains the following data:

SELECT * FROM hive_map ORDER BY col_int;
+---------+---------------+
| col_int | col_map       |
+---------+---------------+
|       1 | {"a":1,"b":2} |
|       2 | {"c":3}       |
|       3 | {"d":4,"e":5} |
+---------+---------------+

After a Hive catalog is created in your cluster, you can use this catalog and the map_size() function to obtain the number of elements in each row of the col_map column.

select map_size(col_map) from hive_map order by col_int;
+-------------------+
| map_size(col_map) |
+-------------------+
|                 2 |
|                 1 |
|                 2 |
+-------------------+
3 rows in set (0.05 sec)