MAP_AGG - MaxCompute - Alibaba Cloud Documentation Center

Returns a map that is created by using a and b. a is the key in the map. b is the value of the key in the map. If the key in the map is null, the key is ignored. If the key field has duplicate values, one of the values is randomly retained.

Usage notes

MaxCompute V2.0 provides additional functions. If the functions that you use involve new data types that are supported in the MaxCompute V2.0 data type edition, you must run a SET command to enable the MaxCompute V2.0 data type edition. The new data types include TINYINT, SMALLINT, INT, FLOAT, VARCHAR, TIMESTAMP, and BINARY.

Session level: To enable the MaxCompute V2.0 data type edition, you must add set odps.sql.type.system.odps2=true; before the SQL statement that you want to execute, and commit and execute them together.
Project level: The project owner can enable the MaxCompute V2.0 data type edition for the project based on the project requirements. The configuration takes effect after 10 to 15 minutes. To enable the MaxCompute V2.0 data type edition at the project level, run the following command:
```
setproject odps.sql.type.system.odps2=true;
```
For more information about setproject, see Project operations. For more information about the precautions that you must take when you enable the MaxCompute V2.0 data type edition at the project level, see Data type editions.

If you use an SQL statement that includes multiple aggregate functions and resources in your project are insufficient, a memory overflow issue may occur. We recommend that you optimize the SQL statement or purchase computing resources based on your business requirements.

Syntax

map<K, V> map_agg(K a, V b);

Parameters

a: an input field that is used as the key in the map.
b: an input field that is used as the value in the map.

Return value

A new map that is created by using a and b is returned.

Examples

select map_agg(a, b) from
        values (1L, 'apple'), (2L, 'hi'), (null, 'good'), (1L, 'pie') t(a, b);

The following result is returned:

+------------------------+
| _c0                    |
+------------------------+
| {"2":"hi","1":"apple"} |
+------------------------+

Related functions

MAP_AGG is an aggregate function. For more information about the functions that are used to calculate the average value of multiple input records and to aggregate parameters, see Aggregate functions.