Oracle/PLSQL: Functions,Procedures,Triggers

Oracle/PLSQL: Creating Functions

---

In Oracle, you can create your own functions.

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.

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.

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

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

Oracle/PLSQL: Creating Procedures

---

In Oracle, you can create your own procedures.

The syntax for a procedure is:

CREATE [OR REPLACE] PROCEDURE procedure_name
    [ (parameter [,parameter]) ]
IS
    [declaration_section]
BEGIN
    executable_section
[EXCEPTION
    exception_section]
END [procedure_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.

The following is a simple example of a procedure:

CREATE OR REPLACE Procedure UpdateCourse
   ( name_in IN varchar2 )
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;

insert into student_courses
( course_name,
  course_number)
values ( name_in,
                cnumber );

commit;

close c1;

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

This procedure is called UpdateCourse. It has one parameter called name_in. The procedure will lookup the course_number based on course name. If it does not find a match, it defaults the course number to 99999. It then inserts a new record into the student_courses table.

Oracle/PLSQL Topics: Creating Triggers

---

Insert Triggers:

BEFORE INSERT Trigger

AFTER INSERT Trigger

Update Triggers:

BEFORE UPDATE Trigger

AFTER UPDATE Trigger

Delete Triggers:

BEFORE DELETE Trigger

AFTER DELETE Trigger

Drop Triggers:

Drop a Trigger

Disable/Enable Triggers:

Disable a Trigger

Disable all Triggers on a table

Enable a Trigger

Enable all Triggers on a table