This topic describes the extension functions provided by Hologres.

Hologres is compatible with PostgreSQL. The functions supported by Hologres are a subset of the PostgreSQL functions. You can use Hologres functions in the same way as the PostgreSQL functions. For more information, see Mathematical functions. In actual use, PostgreSQL functions may not meet all your business requirements. Hologres provides some extension functions to simplify your business development, as listed in the following table.

Function Category Internal table Foreign table
APPROX_COUNT_DISTINCT Aggregate function Supported Supported
USER_DISPLAY_NAME Username conversion function N/A N/A
HG_USER_DISPLAY_NAME_TO ID Username conversion function N/A N/A
GET_JSON_OBJECT Hive-compatible function Supported Supported
MAX_PT MaxCompute-compatible function Not supported Supported
HG_CREATE_TABLE_LIKE Tool function N/A N/A
HG_UPDATE_DATABASE_PROPERTY Tool function N/A N/A
SET_TABLE_PROPERTY Tool function Supported Supported
HG_SHARD_ID_FOR_DISTRIBUTION_KEY Tool function Supported Not supported