Function

A function is a subprogram that returns a single value. You must declare and define a function before invoking it. You can either declare and define it at the same time, or you can declare it first and then define it later in the same block, subprogram, or package. A function invocation, or function call, is an expression.

Topics:

• Syntax

• Semantics

• Examples

• Related Topics

Syntax

function_declaration ::=

function_heading ::=

See:

• datatype ::=

• parameter_declaration ::=

function_definition ::=

See:

• body ::=

• declare_section ::=

relies_on_clause ::=

Semantics

body

The required executable part of the function and, optionally, the exception-handling part of the function.

At least one execution path must lead to a RETURN statement in the executable part of the function; otherwise, a run-time error occurs.

declare_section

The optional declarative part of the function. Declarations are local to the function, can be referenced in body, and cease to exist when the function completes execution.

DETERMINISTIC

Specify DETERMINISTIC to indicate that the function returns the same result value whenever it is invoked with the same values for its parameters. This helps the optimizer avoid redundant function calls: If a stored function was invoked previously with the same arguments, the optimizer can elect to use the previous result.

Do not specify DETERMINISTIC for a function whose result depends on the state of session variables or schema objects, because results might vary across calls. Instead, consider making the function result-cached (see "Making Result-Cached Functions Handle Session-Specific Settings" and "Making Result-Cached Functions Handle Session-Specific Application Contexts").

Only DETERMINISTIC functions can be invoked from a function-based index or a materialized view that has query-rewrite enabled. For more information and possible limitations of the DETERMINISTIC option, see "CREATE FUNCTION Statement".

function_declaration

Declares a function, but does not define it. The definition must appear later in the same block, subprogram, or package as the declaration.

A function declaration is also called a function specification, or function spec.

function_definition

Either defines a function that was declared earlier or both declares and defines a function.

function_name

The name that you give to the function that you are declaring or defining.

IN, OUT, IN OUT

Parameter modes that define the action of formal parameters. For summary information about parameter modes, see Table 8-1.

NOCOPY

Specify NOCOPY to instruct the database to pass this argument as fast as possible. This clause can significantly enhance performance when passing a large value like a record, an associative array, or a varray to an OUT or IN OUT parameter. IN parameter values are always passed NOCOPY.

• When you specify NOCOPY, assignments made to a package variable may show immediately in this parameter, or assignments made to this parameter may show immediately in a package variable, if the package variable is passed as the actual assignment corresponding to this parameter.

• Similarly, changes made either to this parameter or to another parameter may be visible immediately through both names if the same variable is passed to both.

• If the function is exited with an unhandled exception, then any assignment made to this parameter may be visible in the caller's variable.

These effects might not occur on any particular call. You should use NOCOPY only when these effects would not matter.

parameter_name

The name of the formal parameter that you are declaring, which you can reference in body.

PARALLEL_ENABLE

Enables the function to be used safely in slave sessions of parallel DML evaluations.

PIPELINED

PIPELINED specifies to return the results of a table function iteratively. A table function returns a collection type (a nested table or varray) with elements that are SQL data types. You can query table functions using the TABLE keyword before the function name in the FROM clause of a SQL query. For more information, see "Performing Multiple Transformations with Pipelined Table Functions".

relies_on_clause

Specifies the data sources on which the results of the function depend. Each data_source is the name of either a database table or view.

RESULT_CACHE

Causes the results of the function to be cached. For more information, see "PL/SQL Function Result Cache".

RETURN datatype

For datatype, specify the data type of the return value of the function. The return value can have any data type supported by PL/SQL.

Restriction on datatype You cannot constrain this data type (with NOT NULL, for example).

Examples

• Example 8-2, "Declaring, Defining, and Invoking a Simple PL/SQL Function"

• Example 5-44, "Returning a Record from a Function"

Related Topics

In this chapter:

• "Parameter"

• "Procedure"

In other chapters:

• Chapter 8, "PL/SQL Subprograms"