Help Center/ MapReduce Service/ Developer Guide (Normal_3.x)/ Impala Development Guide (Normal Mode)/ Application Development/ User-defined Functions
Updated on 2022-08-16 GMT+08:00
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User-defined Functions

When built-in functions of Impala cannot meet requirements, you can compile user-defined functions (UDFs) and use them for query.

According to implementation methods, UDFs are classified as follows:

  • Common UDFs: used to perform operations on a single data row and export a single data row.
  • User-defined aggregating functions (UDAFs): used to input multiple data rows and export a single data row.
  • User-defined table-generating functions (UDTFs): used to perform operations on a single data row and export multiple data rows. Impala does not support this type of UDFs.

According to use methods, UDFs are classified as follows:

  • Temporary functions: used only in the current session and must be recreated after a session restarts.
  • Permanent functions: used in multiple sessions. You do not need to create them every time a session restarts.

Impala supports development of Java UDFs and reuse of UDFs developed by Hive. The prerequisite is that the data types supported by Impala are used. For details about the data types supported by Impala, visit http://impala.apache.org/docs/build3x/html/topics/impala_datatypes.html.

In addition, Impala supports UDFs written in C++, which provides better performance than Java UDFs.

Example

The following is an example of reusing the lower() function:

[localhost:21000] > create database udfs;
[localhost:21000] > use udfs;
[localhost:21000] > create function my_lower(string)
returns string location '/user/hive/udfs/hive.jar'
symbol='org.apache.hadoop.hive.ql.udf.UDFLower';
[localhost:21000] > select my_lower('Some String NOT ALREADY LOWERCASE');
+----------------------------------------------------+
| udfs.my_lower('some string not already lowercase') |
+----------------------------------------------------+
| some string not already lowercase |
+----------------------------------------------------+
Returned 1 row(s) in 0.11s
[localhost:21000] > create table t2 (s string);
[localhost:21000] > insert into t2 values ('lower'),('UPPER'),('Init cap'),('CamelCase');
Inserted 4 rows in 2.28s
[localhost:21000] > select * from t2;
+-----------+
| s |
+-----------+
| lower |
| UPPER |
| Init cap |
| CamelCase |
+-----------+
Returned 4 row(s) in 0.47s
[localhost:21000] > select my_lower(s) from t2;
+------------------+
| udfs.my_lower(s) |
+------------------+
| lower |
| upper |
| init cap |
| camelcase |
+------------------+
Returned 4 row(s) in 0.54s
Parent topic: Application Development