# CREATE FUNCTION Statement Confluent Cloud for Apache Flink® enables registering custom user-defined functions (UDFs) by using the CREATE FUNCTION statement. After you register your UDFs in a Flink database, you can use them in your SQL queries. ## Syntax ```sql CREATE FUNCTION AS USING JAR 'confluent-artifact://' [USING CONNECTIONS ('' [, ...])]; ``` ## Description Register a user-defined function (UDF) in the current database. The optional `USING CONNECTIONS` clause binds one or more [connection objects](../../../integrations/connections/overview.md#connections-overview) to the UDF, enabling [external connectivity](../../concepts/user-defined-functions.md#flink-sql-udfs-external-connectivity) so the function can call external systems at runtime. Provide one or more connection names, separated by commas. The connection name must match the prefix that the UDF uses with `FunctionContext.getJobParameter()`. For example, use `USING CONNECTIONS ('my_external_service')` for a `my_external_service.endpoint` parameter. - To remove a UDF from the current database, use [DROP FUNCTION](drop-function.md#flink-sql-drop-function). - To view the UDFs in the current database, use [SHOW FUNCTIONS](show.md#flink-sql-show-functions). #### NOTE UDFs are immutable. Flink has no `ALTER FUNCTION` or `CREATE OR REPLACE FUNCTION` statement, so to update a UDF, drop it and create a new function that points to the updated artifact. Dropping a function that other statements depend on can break the other statements. To ensure your statements work, see [Update a UDF safely](../../how-to-guides/create-udf.md#flink-sql-update-udf). ## Related content - [Create a User-Defined Function](../../how-to-guides/create-udf.md#flink-sql-create-udf) - [Update a UDF safely](../../how-to-guides/create-udf.md#flink-sql-update-udf) - [DROP FUNCTION](drop-function.md#flink-sql-drop-function) - [SHOW FUNCTIONS](show.md#flink-sql-show-functions) - [confluent flink artifact create](https://docs.confluent.io/confluent-cli/current/command-reference/flink/artifact/confluent_flink_artifact_create.html) #### NOTE This website includes content developed at the [Apache Software Foundation](https://www.apache.org/) under the terms of the [Apache License v2](https://www.apache.org/licenses/LICENSE-2.0.html).