|Oracle® Database PL/SQL User's Guide and Reference
10g Release 2 (10.2)
|PDF · Mobi · ePub|
A function is a subprogram that can take parameters and return a single value. A function has two parts: the specification and the body. The specification (spec for short) begins with the keyword
FUNCTION and ends with the
RETURN clause, which specifies the datatype of the return value. Parameter declarations are optional. Functions that take no parameters are written without parentheses. The function body begins with the keyword
AS) and ends with the keyword
END followed by an optional function name.
The function body has three parts: an optional declarative part, an executable part, and an optional exception-handling part. The declarative part contains declarations of types, cursors, constants, variables, exceptions, and subprograms. These items are local and cease to exist when you exit the function. The executable part contains statements that assign values, control execution, and manipulate data. The exception-handling part contains handlers that deal with exceptions raised during execution. For more information, see "Understanding PL/SQL Functions". For an example of a function declaration, see Example 9-3.
Note that the function declaration in a PL/SQL block or package is not the same as creating a function in SQL. For information on the
FUNCTION SQL statement, see Oracle Database SQL Reference.
function specification ::=
function declaration ::=
function body ::=
parameter declaration ::=
A type specifier. For the syntax of
datatype, see "Constant and Variable Declaration".
A hint that helps the optimizer avoid redundant function calls. If a stored function was called previously with the same arguments, the optimizer can elect to use the previous result. The function result should not depend on the state of session variables or schema objects. Otherwise, results might vary across calls. Only
DETERMINISTIC functions can be called 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 the
FUNCTION statement in the Oracle Database SQL Reference. See also the
INDEX statement in Oracle Database SQL Reference.
Associates an exception with a sequence of statements, which is executed when that exception is raised. For the syntax of
exception_handler, see "Exception Definition".
An arbitrarily complex combination of variables, constants, literals, operators, and function calls. The simplest expression consists of a single variable. When the declaration is elaborated, the value of
expression is assigned to the parameter. The value and the parameter must have compatible datatypes.
Specifies the name you choose for the function.
IN, OUT, IN OUT
Parameter modes that define the behavior of formal parameters. An
IN parameter passes values to the subprogram being called. An
OUT parameter returns values to the caller of the subprogram. An
OUT parameter passes initial values to the subprogram being called, and returns updated values to the caller.
Declares a program object. For its syntax, see "Block Declaration".
A compiler hint (not directive) that allows the PL/SQL compiler to pass
OUT parameters by reference instead of by value (the default). The function can run faster, because it does not have to make temporary copies of these parameters, but the results can be different if the function ends with an unhandled exception. For more information, see "Using Default Values for Subprogram Parameters".
Declares that a stored function can be used safely in the slave sessions of parallel DML evaluations. The state of a main (logon) session is never shared with slave sessions. Each slave session has its own state, which is initialized when the session begins. The function result should not depend on the state of session (
static) variables. Otherwise, results might vary across sessions. For information on the
PARALLEL_ENABLE option, see the
FUNCTION statement in the Oracle Database SQL Reference.
A formal parameter, a variable declared in a function spec and referenced in the function body.
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 datatypes. 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 "Setting Up Transformations with Pipelined Functions".
Marks a function as autonomous. An autonomous transaction is an independent transaction started by the main transaction. Autonomous transactions let you suspend the main transaction, do SQL operations, commit or roll back those operations, then resume the main transaction. For more information, see "Doing Independent Units of Work with Autonomous Transactions".
Declares a procedure. For the syntax of
procedure_declaration, see "Procedure Declaration".
RETURN clause, which specifies the datatype of the return value.
Specifies a user-defined datatype. For
its syntax, see "Block Declaration".
IN parameters to default values.
A function is called as part of an expression:
promotable := sal_ok(new_sal, new_title) AND (rating > 3);
To be callable from SQL statements, a stored function must obey certain rules that control side effects. See "Controlling Side Effects of PL/SQL Subprograms".
In a function, at least one execution path must lead to a
RETURN statement. Otherwise, you get a
function returned without value error at run time. The
RETURN statement must contain an expression, which is evaluated when the
RETURN statement is executed. The resulting value is assigned to the function identifier, which acts like a variable.
You can write the function spec and body as a unit. Or, you can separate the function spec from its body. That way, you can hide implementation details by placing the function in a package. You can define functions in a package body without declaring their specs in the package spec. However, such functions can be called only from inside the package.
Inside a function, an
IN parameter acts like a constant; you cannot assign it a value. An
OUT parameter acts like a local variable; you can change its value and reference the value in any way. An
OUT parameter acts like an initialized variable; you can assign it a value, which can be assigned to another variable. For information about the parameter modes, see Table 8-1.
Avoid using the
OUT modes with functions. The purpose of a function is to take zero or more parameters and return a single value. Functions should be free from side effects, which change the values of variables not local to the subprogram.
For examples, see the following: