Oracle/PLSQL: Creating Functions

In Oracle, you can create your own functions.

译：在ORACLE中，你可以创建你自己的方法。

The syntax for a function is:

CREATE [OR REPLACE] FUNCTION function_name
    [ (parameter [,parameter]) ]
    RETURN return_datatype
IS | AS
    [declaration_section]
BEGIN
    executable_section
[EXCEPTION
    exception_section]
END [function_name];

 

When you create a procedure or function, you may define parameters. There are three types of parameters that can be declared:

1.IN - The parameter can be referenced by the procedure or function. The value of the parameter can not be overwritten by the procedure or function.

2.OUT - The parameter can not be referenced by the procedure or function, but the value of the parameter can be overwritten by the procedure or function.

3.IN OUT - The parameter can be referenced by the procedure or function and the value of the parameter can be overwritten by the procedure or function.

译：在你创建一个过程或者是方法时，可能会定义参数。这里有三种类型的参数可被定义：

1、IN -该参数可以被过程或者是方法引用。但该参数的值不可以被过程或者是方法重写。

2、 OUT -该参数不可以被过程或者是方法引用。但该参数的值可以被过程或者是方法重写。

3、 IN OUT -该参数既可以被过程或者是方法引用。该参数的值也可以被过程或者是方法重写。

The following is a simple example of a function:

CREATE OR REPLACE Function FindCourse
   ( name_in IN varchar2 )
   RETURN number
IS
    cnumber number;

    cursor c1 is
    select course_number
      from courses_tbl
      where course_name = name_in;

BEGIN

open c1;
fetch c1 into cnumber;

if c1%notfound then
     cnumber := 9999;
end if;

close c1;

RETURN cnumber;

EXCEPTION
WHEN OTHERS THEN
      raise_application_error(-20001,'An error was encountered - '||SQLCODE||' -ERROR- '||SQLERRM);
END;

This function is called FindCourse. It has one parameter called name_in and it returns a number. The function will return the course number if it finds a match based on course name. Otherwise, it returns a 99999.

译：方法名为FindCourse，它有一个名为name_in的参数并且结果返回一个数字。如果它找到一个与课程名相同，那么就返回该课程号，否则就返回99999。

You could then reference your new function in an SQL statement as follows:

译：你可以在SQL语句这样引用你的新方法：

select course_name, FindCourse(course_name) as course_id
from courses
where subject = 'Mathematics';