PL/SQL Assistance Needed with Trigger - sql

Question

I am in the process of trying to create a trigger that when a record is inserted into the employee table(a new employee), the trigger fires and inserts a record into the employee_dept_history table as 'N/A' (since this employee is new and has no previous department). Also, if a current employee switches departments the trigger should insert a record in the employee_dept_history table and the employees depatment_id changes. I am having problems creating this trigger.I was wondering if someone could lead me to the right direction with my code. I can't get the below trigger to display 'N/A'. How could I go about making this trigger work? Do I need to create local variables for the new and old department?
CREATE OR REPLACE TRIGGER employee_dept_trigger
BEFORE INSERT OR UPDATE ON employee
FOR EACH ROW
BEGIN
INSERT INTO employee_dept_history
VALUES(:NEW.employee_id,
:NEW.employee_name,
from_department_name (NEEDS TO OUTPUT 'N/A'),
to_department_name,
sysdate);
END employee_dept_trigger;
The EMPLOYEE_DEPT_HISTORY table looks like:
CREATE TABLE empployee_dept_history
(
EMPLOYEE_ID NUMBER(4)
EMPLOYEE_NAME VARCHAR2(50)
FROM_DEPARTMENT_NAME VARCHAR2(50)
TO_DEPARTMENT_NAME VARCHAR2(50)
OPERATION_TIME DATE
);
The EMPLOYEE table:
(
EMPLOYEE_ID NUMBER(4)
EMPLOYEE_NAME VARCHAR2(20)
JOB VARCHAR2(50)
MANAGER_ID NUMBER(4)
HIRE_DATE DATE
SALARY NUMBER(9)
COMMISION NUMBER(9)
DEPARTMENT_ID NUMBER(4)
);

Answer 1

Note: This answer is similar to the other two, but I'll post it anyway because it defines the trigger differently in a way that may be useful. Please note that I've up-voted the other two answers as they'll do the job nicely.
First, if you're only interested in changes to the DEPARTMENT_ID column, you can specify that in your trigger definition:
CREATE OR REPLACE TRIGGER employee_dept_trigger
BEFORE INSERT OR UPDATE OF department_id ON employee
FOR EACH ROW
....
A trigger can use the "automatic" logical values INSERTING and UPDATING to determine if an insert or an update called it. You can use the INSERTING value to indicate that this is a new employee:
IF INSERTING THEN
-- set old department name = 'N/A'
ELSE
-- set old department name = whatever
END IF;
Your question doesn't describe where the department name comes from, so this example descends into pseudocode when it comes to the department names:
CREATE OR REPLACE TRIGGER employee_dept_trigger
BEFORE INSERT OR UPDATE OF department_id ON employee
FOR EACH ROW
BEGIN
IF INSERTING THEN
-- New employee
INSERT INTO employee_dept_history VALUES (
:NEW.employee_id,
:NEW.employee_name,
'N/A',
(SELECT department_name from ...), <-- based on :NEW.department_id
SYSDATE);
ELSE
-- Existing employee
INSERT INTO employee_dept_history VALUES (
:NEW.employee_id,
:NEW.employee_name,
(SELECT department_name from ...), <-- based on :OLD.department_id
(SELECT department_name from ...), <-- based on :NEW.department_id
SYSDATE);
END IF;
END employee_dept_trigger;

Answer 2

It's either
CREATE OR REPLACE TRIGGER employee_dept_trigger
BEFORE INSERT OR UPDATE ON employee
FOR EACH ROW
DECLARE
from_department_name varchar(255);
to_department_name varchar(255);
BEGIN
select from DEPARTMENT where DEPARTMENT_ID=:NEW.DEPARTMENT_ID into to_department_name;
IF INSERTING THEN
INSERT INTO employee_dept_history
VALUES(:NEW.employee_id,
:NEW.employee_name,
'N/A',
to_department_name,
sysdate);
end if;
IF UPDATING THEN
select from DEPARTMENT where DEPARTMENT_ID=:OLD.DEPARTMENT_ID into from_department_name;
INSERT INTO employee_dept_history
VALUES(:NEW.employee_id,
:NEW.employee_name,
from_department_name ,
to_department_name,
sysdate);
end if;
END employee_dept_trig;
or I don't understand your question.

Answer 3

You probably want something like this:
CREATE OR REPLACE TRIGGER employee_dept_trigger
BEFORE INSERT OR UPDATE ON employee
FOR EACH ROW
BEGIN
IF INSERTING THEN
INSERT INTO employee_dept_history
VALUES(:NEW.employee_id,
:NEW.employee_name,
'N/A',
:NEW.DEPARTMENT_ID,
sysdate);
ELSE
INSERT INTO employee_dept_history
VALUES(:NEW.employee_id,
:NEW.employee_name,
:OLD.DEPARTMENT_ID,
:NEW.DEPARTMENT_ID,
sysdate);
END IF;
END employee_dept_trigger;
It won't be quite right yet though as you haven't indicated where the department name comes from. I've used department id just to give you an idea..