This topic describes the extension functions provided by Hologres.
Hologres is compatible with PostgreSQL. You can use Hologres functions in the same way as PostgreSQL functions.
The functions supported by Hologres are a subset of the PostgreSQL functions. In actual use, PostgreSQL functions may not meet all your business requirements. Hologres provides some extension functions to simplify your business development.
The following table describes the extension functions that are supported by Hologres.
| Category | References | Scenario | Support for internal tables | Support for foreign tables | Supported version |
|---|---|---|---|---|---|
| Spatial functions | PostGIS for geographic information analysis | Return spatial features, including objects, indexes, functions, and operators. | Yes | No | V0.10 and later |
| Vector processing functions | Vector processing based on Proxima | Provide a high-performance vector search feature. | Yes | No | V0.10 and later |
| APPROX_COUNT_DISTINCT | Calculates the approximate number of rows that have distinct values in a column of a table and provides better performance than the COUNT DISTINCT function. | Yes | Yes | V0.10 and later | |
| Traffic analysis functions | Funnel analysis functions | Perform funnel and retention analysis and calculate the conversion rate (CVR). | Yes | No | V0.9 and later |
| Intended user identification functions | Identify users that meet specific conditions from a table and reduce the resource consumption of JOIN statements. | Yes | No | V0.10 and later | |
| Roaring bitmap functions | Use efficient compressed bitmaps and can be used for deduplication, tag-based filtering, and quasi-real-time user persona analysis. | Yes | No | V0.9 and later | |
| Username conversion functions | USER_DISPLAY_NAME | Convert the ID of an account in Hologres into the email address of an Alibaba Cloud account or a string that indicates a RAM user. | N/A | N/A | All versions |
| HG_DISPLAY_NAME_TO _ID | Convert the email address of an Alibaba Cloud account or a string that indicates a RAM user into the ID of an account in Hologres. | N/A | N/A | All versions | |
| Hive-compatible function | GET_JSON_OBJECT | Parses a value into a JSON object. | Yes | No | V0.9 and later |
| MaxCompute-compatible function | MAX_PT | Queries the name of the largest partitioned table for a MaxCompute table of Hologres. | Yes | Yes | V0.9 and later |
| Tool functions | HG_VERSION | Queries the information about the current version of Hologres. | N/A | N/A | All versions |
| HG_UPDATE_DATABASE_PROPERTY | Modifies the properties of a database. | N/A | N/A | All versions | |
| SET_TABLE_PROPERTY | Sets table properties and is executed with the CREATE TABLE statement. | Yes | N/A | All versions |