UDF Sample Code and Operations

Updated on 2024-11-29 GMT+08:00

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Complete UDF Sample Code

For details, see "IoTDB UDF Program" in .

Procedure

Register a UDF.

Register a UDF with a full class name com.huawei.bigdata.iotdb.UDTFExample as follows:
1. Pack the project into a JAR file. To use Maven to manage your project, refer to step "Build a JAR file" in "Registering a UDF" in .
2. Log in to the node where IoTDBServer is located as user root, run su - omm to switch to user omm, and import the JAR package obtained in 1.a to the $BIGDATA_HOME/FusionInsight_IoTDB_*/install/FusionInsight-IoTDB-*/iotdb/ext/udf directory.
  NOTICE:
  
  During cluster deployment, ensure that a corresponding JAR package exists in the UDF JAR package path of each IoTDBserver node. You can modify the IoTDB configuration file udf_root_dir to specify the root path for the UDF to load the JAR package.
3. Execute the following SQL statement to register the UDF:
  CREATE FUNCTION <UDF-NAME> AS '<UDF-CLASS-FULL-PATHNAME>'
  
  For example, to register a UDF named example, execute the following statement:
```
CREATE FUNCTION example AS 'com.huawei.bigdata.iotdb.UDTFExample'
```
  Because IoTDB UDF instances are dynamically loaded through the reflection technology, you do not need to restart the server during the UDF registration process.
  NOTICE:
  - UDF function names are case insensitive.
  - Ensure that the function name given to the UDF is different from all built-in function names. A UDF with the same name as a built-in function cannot be registered.
  - It is recommended that you do not use classes that have the same class name but different function logic in different JAR packages. For example, in UDF(UDAF/UDTF): udf1, udf2, the JAR package of udf1 is udf1.jar and the JAR package of udf2 is udf2.jar. Assume that both JAR packages contain the com.huawei.bigdata.iotdb.UDTFExample class. If you use two UDFs in the same SQL statement at the same time, the system will randomly load either of them and may cause inconsistency in UDF execution behavior.
Query the UDF.
- Basic SQL syntax supported:
  - SLIMIT / SOFFSET
  - LIMIT / OFFSET
  - NON ALIGN
  - Queries with value filters
  - Queries with time filters
- Queries with aligned time series
  Currently, aligned time series are not supported in UDF queries. An error message is reported if you use UDF queries with aligned time series selected.
- Queries with an asterisk (*) in SELECT clauses
  Assume that there are two time series (root.sg.d1.s1 and root.sg.d1.s2) in the system.
  - Execute SELECT example(*) from root.sg.d1.
    Then the result set will include the results of example (root.sg.d1.s1) and example (root.sg.d1.s2).
  - Execute SELECT example(s1, *) from root.sg.d1.
    Then the result set will include the results of example(root.sg.d1.s1, root.sg.d1.s1) and example(root.sg.d1.s1, root.sg.d1.s2).
  - Execute SELECT example(*, *) from root.sg.d1.
    Then the result set will include the results of example(root.sg.d1.s1, root.sg.d1.s1), example(root.sg.d1.s2, root.sg.d1.s1), example(root.sg.d1.s1, root.sg.d1.s2), and example(root.sg.d1.s2, root.sg.d1.s2).
- Queries with key-value pair attributes in UDF parameters
  You can pass any number of key-value pair parameters to the UDF when constructing a UDF query. The key and value in the key-value pair need to be enclosed in single or double quotes. Note that key-value pair parameters can be passed in only after all time series have been passed in. Example:
```
SELECT example(s1, 'key1'='value1', 'key2'='value2'), example(*, 'key3'='value3') FROM root.sg.d1;
SELECT example(s1, s2, 'key1'='value1', 'key2'='value2') FROM root.sg.d1;
```
- Showing all registered UDFs
  SHOW FUNCTIONS
Deregister the UDF.

The following shows the SQL syntax of how to deregister a UDF:

DROP FUNCTION <UDF-NAME>

To deregister the UDF named example, execute the following statement:
```
DROP FUNCTION example
```

Parent topic: UDFs

Previous topic: UDF Overview

Next topic: IoTDB Data Import and Export

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