|Oracle9i SQL Reference
Release 2 (9.2)
Part Number A96540-01
SQL Statements: CREATE CLUSTER to CREATE JAVA, 9 of 12
FUNCTION statement to create a standalone stored function or a call specification. (You can also create a function as part of a package using the
A stored function (also called a user function) is a set of PL/SQL statements you can call by name. Stored functions are very similar to procedures, except that a function returns a value to the environment in which it is called. User functions can be used as part of a SQL expression.
A call specification declares a Java method or a third-generation language (3GL) routine so that it can be called from SQL and PL/SQL. The call specification tells Oracle which Java method, or which named function in which shared library, to invoke when a call is made. It also tells Oracle what type conversions to make for the arguments and return value.
Before a stored function can be created, the user
SYS must run a SQL script that is commonly called
DBMSSTDX.SQL. The exact name and location of this script depend on your operating system.
To create a function in your own schema, you must have the
PROCEDURE system privilege. To create a function in another user's schema, you must have the
PROCEDURE system privilege. To replace a function in another user's schema, you must have the
PROCEDURE system privilege.
To invoke a call specification, you may need additional privileges (for example,
EXECUTE privileges on C library for a C call specification).
To embed a
FUNCTION statement inside an Oracle precompiler program, you must terminate the statement with the keyword
END-EXEC followed by the embedded SQL statement terminator for the specific language.
REPLACE to re-create the function if it already exists. Use this clause to change the definition of an existing function without dropping, re-creating, and regranting object privileges previously granted on the function. If you redefine a function, Oracle recompiles it.
Users who had previously been granted privileges on a redefined function can still access the function without being regranted the privileges.
If any function-based indexes depend on the function, Oracle marks the indexes
ALTER FUNCTION for information on recompiling functions
Specify the schema to contain the function. If you omit
schema, Oracle creates the function in your current schema.
Specify the name of the function to be created. If creating the function results in compilation errors, Oracle returns an error. You can see the associated compiler error messages with the
Restrictions on user-defined functions:
User-defined functions cannot be used in situations that require an unchanging definition. Thus, you cannot use user-defined functions:
CHECKconstraint clause of a
DEFAULTclause of a
In addition, when a function is called from within a query or DML statement, the function cannot:
SELECTstatement. However, a function called from a subquery in a DML statement can write to the database.
Except for the restriction on
OUT parameters, Oracle enforces these restrictions not only for the function called directly from the SQL statement, but also for any functions that function calls, and on any functions called from the SQL statements executed by that function or any function it calls.
Specify the name of an argument to the function. If the function does not accept arguments, you can omit the parentheses following the function name.
Restriction on function arguments: If you are creating an aggregate function, you can specify only one argument.
IN to indicate that you must supply a value for the argument when calling the function. This is the default.
OUT to indicate that the function will set the value of the argument.
OUT to indicate that a value for the argument can be supplied by you and may be set by the function.
NOCOPY to instruct Oracle to pass this argument as fast as possible. This clause can significantly enhance performance when passing a large value like a record, an index-by table, or a varray to an
OUT parameter. (
IN parameter values are always passed
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.
These effects may or may not occur on any particular call. You should use
NOCOPY only when these effects would not matter.
For datatype, specify the datatype of the function's return value. Because every function must return a value, this clause is required. The return value can have any datatype supported by PL/SQL.
Oracle SQL does not support calling of functions with boolean parameters or returns. Therefore, if your user-defined functions will be called from SQL statements, you must design them to return numbers (0 or 1) or character strings ('
The datatype cannot specify a length, precision, or scale. Oracle derives the length, precision, or scale of the return value from the environment from which the function is called.
If the return type is
SYS.AnyDataSet and you intend to use the function in the
FROM clause of a query, then you must also specify the
PIPELINED clause and define a describe method (
ODCITableDescribe) as part of the implementation type of the function.
invoker_rights_clause lets you specify whether the function executes with the privileges and in the schema of the user who owns it or with the privileges and in the schema of
This clause also determines how Oracle resolves external names in queries, DML operations, and dynamic SQL statements in the function.
CURRENT_USERif you want the function to execute with the privileges of
CURRENT_USER. This clause creates an invoker-rights function.
This clause also specifies that external names in queries, DML operations, and dynamic SQL statements resolve in the schema of
CURRENT_USER. External names in all other statements resolve in the schema in which the function resides.
DEFINERif you want the function to execute with the privileges of the owner of the schema in which the function resides, and that external names resolve in the schema where the function resides. This is the default and creates a defined-rights function.
DETERMINISTIC to indicate that the function returns the same result value whenever it is called with the same values for its arguments.
You must specify this keyword if you intend to call the function in the expression of a function-based index or from the query of a materialized view that is marked
REWRITE. When Oracle encounters a deterministic function in one of these contexts, it attempts to use previously calculated results when possible rather than re-executing the function.
Do not specify this clause to define a function that uses package variables or that accesses the database in any way that might affect the function's return result. The results of doing so will not be captured if Oracle chooses not to reexecute the function.
The following semantic rules govern the use of the
DETERMINISTICin the package specification, but not in the package body.
DETERMINISTICa private subprogram (declared inside another subprogram or inside a package body).
DETERMINISTICsubprogram can call another subprogram whether the called program is declared
PARALLEL_ENABLE is an optimization hint indicating that the function can be executed from a parallel execution server of a parallel query operation. The function should not use session state, such as package variables, as those variables may not be shared among the parallel execution servers.
BYclause is used only with functions that have a
CURSORargument type. It lets you define the partitioning of the inputs to the function from the
Partitioning the inputs to the function affects the way the query is parallelized when the function is used as a table function (that is, in the
FROM clause of the query).
ANY indicates that the data can be partitioned randomly among the parallel execution servers. Alternatively, you can specify
HASH partitioning on a specified column list.
streaming_clauselets you order or cluster the parallel processing by a specified column list.
The columns specified in all of these optional clauses refer to columns that are returned by the
CURSOR argument of the function.
Oracle9i Application Developer's Guide - Fundamentals, Oracle9i Data Cartridge Developer's Guide, and PL/SQL User's Guide and Reference for more information on user-defined aggregate functions
PIPELINED to instruct Oracle to return the results of a table function iteratively. A table function returns a collection type (a nested table or varray). You query table functions by using the
TABLE keyword before the function name in the
FROM clause of the query. For example:
Oracle then returns rows as they are produced by the function.
IS...), the PL/SQL function body should use the
PIPEkeyword. This keyword instructs Oracle to return single elements of the collection out of the function, instead of returning the whole collection as a single value.
implementation_typeclause if you want to predefine an interface containing the start, fetch, and close operations. The implementation type must implement the
ODCITableinterface, and must exist at the time the table function is created. This clause is useful for table functions that will be implemented in external languages such as C++ and Java.
If the return type of the function is
SYS.AnyDataSet, then you must also define a describe method (
ODCITableDescribe) as part of the implementation type of the function.
USING to identify this function as an aggregate function, or one that evaluates a group of rows and returns a single row. You can specify aggregate functions in the
HAVING clause, and
When you specify a user-defined aggregate function in a query, you can treat it as an analytic function (one that operates on a query result set). To do so, use the
USING clause, specify the name of the implementation type of the function. The implementation type must be an object type containing the implementation of the ODCIAggregate routines. If you do not specify
schema, Oracle assumes that the implementation type is in your own schema.
Restriction on the AGGREGATE USING clause: If you specify this clause, you can specify only one input argument for the function.
Use the pl/
sql_subprogram_body to declare the function in a PL/SQL subprogram body.
Oracle9i Application Developer's Guide - Fundamentals for more information on PL/SQL subprograms and "Using a Packaged Procedure in a Function: Example"
call_spec to map a Java or C method name, parameter types, and return type to their SQL counterparts. In
string' identifies the Java implementation of the method.
EXTERNAL is an alternative way of declaring a C method. This clause has been deprecated and is supported for backward compatibility only. Oracle Corporation recommends that you use the
The following statement creates the function
get_bal on the sample table
oe.orders (the PL/SQL is in italics):
CREATE FUNCTION get_bal(acc_no IN NUMBER) RETURN NUMBER IS acc_bal NUMBER(11,2); BEGIN SELECT order_total INTO acc_bal FROM orders WHERE customer_id = acc_no; RETURN(acc_bal); END; /
get_bal function returns the balance of a specified account.
When you call the function, you must specify the argument
acc_no, the number of the account whose balance is sought. The datatype of
The function returns the account balance. The
RETURN clause of the
FUNCTION statement specifies the datatype of the return value to be
The function uses a
SELECT statement to select the
balance column from the row identified by the argument
acc_no in the
orders table. The function uses a
RETURN statement to return this value to the environment in which the function is called.
The function created in the preceding example can be used in a SQL statement. For example:
The following statement creates PL/SQL standalone function
get_val that registers the C routine
c_get_val as an external function. (The parameters have been omitted from this example; the PL/SQL is in italics.)
CREATE FUNCTION get_val ( x_val IN NUMBER, y_val IN NUMBER, image IN LONG RAW ) RETURN BINARY_INTEGER AS LANGUAGE C NAME "c_get_val" LIBRARY c_utils PARAMETERS (...);
The next statement creates an aggregate function called
SecondMax to aggregate over number values. It assumes that the object type
SecondMaxImpl routines contains the implementations of the
CREATE FUNCTION SecondMax (input NUMBER) RETURN NUMBER PARALLEL_ENABLE AGGREGATE USING SecondMaxImpl;
Oracle9i Data Cartridge Developer's Guide for the complete implementation of type and type body for
You would use such an aggregate function in a query like the following statement, which queries the sample table
SELECT SecondMax(salary), department_id FROM employees GROUP BY department_id HAVING SecondMax(salary) > 9000; SECONDMAX(SALARY) DEPARTMENT_ID ----------------- ------------- 13500 80 17000 90
The following statement creates a function that uses a
DBMS_LOB procedure to return the length of a
CREATE OR REPLACE FUNCTION text_length(a CLOB) RETURN NUMBER DETERMINISTIC IS BEGIN RETURN DBMS_LOB.GETLENGTH(a); END;
"Creating a Function-Based Index on a LOB Column: Example" to see how to use this function to create a function-based index