# CREATE FUNCTION statement

The CREATE FUNCTION statement allows you to create Java functions, which you can then use in an expression.

The function owner and the database owner automatically gain the EXECUTE privilege on the function, and are able to grant this privilege to other users. The EXECUTE privileges cannot be revoked from the function and database owners.

For details on how Derby matches functions to Java methods, see Argument matching.

#### Syntax

    CREATE FUNCTION function-name ( [ FunctionParameter
       [, FunctionParameter] ] * ) RETURNS ReturnDataType [ FunctionElement ] *

#### function-Name

    [ schemaName. ] SQL92Identifier

If schema-Name is not provided, the current schema is the default schema. If a qualified procedure name is specified, the schema name cannot begin with SYS.

#### FunctionParameter

    [ parameter-Name ] DataType

PararameterName must be unique within a function.

The syntax of DataType is described in Data types.

Note: Data-types such as BLOB, CLOB, LONG VARCHAR, LONG VARCHAR FOR BIT DATA, and XML are not allowed as parameters in a CREATE FUNCTION statement.

#### ReturnDataType

    TableType | DataType

The syntax of DataType is described in Data types.

#### TableType

    TABLE( ColumnElement [, ColumnElement ]* )

This is the return type of a table function. Currently, only Derby-style table functions are supported. They are functions which return JDBC ResultSets. For more information, see "Programming Derby-style table functions" in the Java DB Developer's Guide.

At run-time, as values are read out of the user-supplied ResultSet, Derby coerces those values to the data types declared in the CREATE FUNCTION statement. This affects values typed as CHAR, VARCHAR, LONG VARCHAR, CHAR FOR BIT DATA, VARCHAR FOR BIT DATA, LONG VARCHAR FOR BIT DATA, and DECIMAL/NUMERIC. Values which are too long are truncated to the maximum length declared in the CREATE FUNCTION statement. In addition, if a String value is returned in the ResultSet for a column of CHAR type and the String is shorter than the declared length of the CHAR column, Derby pads the end of the String with blanks in order to stretch it out to the declared length.

#### ColumnElement

    SQL92Identifier DataType

The syntax of DataType is described in Data types.

Note: XML is not allowed as the type of a column in the dataset returned by a table function.

#### FunctionElement

     {
    | LANGUAGE { JAVA }
    | DeterministicCharacteristic
    | EXTERNAL NAME string
    | PARAMETER STYLE ParameterStyle
    | { NO SQL | CONTAINS SQL | READS SQL DATA }
    | { RETURNS NULL ON NULL INPUT | CALLED ON NULL INPUT }
     }

#### LANGUAGE

JAVA- the database manager will call the function as a public static method in a Java class.

#### EXTERNAL NAME string

String describes the Java method to be called when the function is executed, and takes the following form:

    class_name.method_name

The External Name cannot have any extraneous spaces.

#### DeterministicCharacteristic

    DETERMINISTIC | NOT DETERMINISTIC

Declares that the function is deterministic, meaning that with the same set of input values, it always computes the same result. The default is NOT DETERMINISTIC. Derby cannot recognize whether an operation is actually deterministic, so you must take care to specify the `DeterministicCharacteristic` correctly.

#### ParameterStyle

    JAVA | DERBY_JDBC_RESULT_SET

The function will use a parameter-passing convention that conforms to the Java language and SQL Routines specification. INOUT and OUT parameters will be passed as single entry arrays to facilitate returning values. Result sets can be returned through additional parameters to the Java method of type java.sql.ResultSet[] that are passed single entry arrays.

Derby does not support long column types (for example Long Varchar, BLOB, and so on). An error will occur if you try to use one of these long column types.

The PARAMETER STYLE is DERBY_JDBC_RESULT_SET if and only if this is a Derby-style table function, that is, a function which returns TableType and which is mapped to a method which returns a JDBC ResultSet. Otherwise, the PARAMETER STYLE must be JAVA.

#### NO SQL, CONTAINS SQL, READS SQL DATA

Indicates whether the function issues any SQL statements and, if so, what type.

CONTAINS SQL
  Indicates that SQL statements that neither read nor modify SQL data can be executed by the function. Statements that are not supported in any function return a different error.
NO SQL
  Indicates that the function cannot execute any SQL statements
READS SQL DATA
  Indicates that some SQL statements that do not modify SQL data can be included in the function. Statements that are not supported in any stored function return a different error. This is the default value.

#### RETURNS NULL ON NULL INPUT or CALLED ON NULL INPUT

Specifies whether the function is called if any of the input arguments is null. The result is the null value.

RETURNS NULL ON NULL INPUT
  Specifies that the function is not invoked if any of the input arguments is null. The result is the null value.
CALLED ON NULL INPUT
  Specifies that the function is invoked if any or all input arguments are null. This specification means that the function must be coded to test for null argument values. The function can return a null or non-null value. This is the default setting.

The function elements may appear in any order, but each type of element can only appear once. A function definition must contain these elements:

- LANGUAGE
- PARAMETER STYLE
- EXTERNAL NAME

#### Example of declaring a scalar function

    CREATE FUNCTION TO_DEGREES
    ( RADIANS DOUBLE )
    RETURNS DOUBLE
    PARAMETER STYLE JAVA
    NO SQL LANGUAGE JAVA
    EXTERNAL NAME 'java.lang.Math.toDegrees'

#### Example of declaring a table function

    CREATE FUNCTION PROPERTY_FILE_READER
    ( FILENAME VARCHAR( 32672 ) )
    RETURNS TABLE
      (
         KEY_COL     VARCHAR( 10 ),
         VALUE_COL VARCHAR( 1000 )
      )
    LANGUAGE JAVA
    PARAMETER STYLE DERBY_JDBC_RESULT_SET
    NO SQL
    EXTERNAL NAME 'vtis.example.PropertyFileVTI.propertyFileVTI'

Parent topic: CREATE statements
Related reference
CREATE INDEX statement
CREATE PROCEDURE statement
CREATE ROLE statement
CREATE SCHEMA statement
CREATE SYNONYM statement
CREATE TABLE statement
CREATE TRIGGER statement
CREATE VIEW statement