Use trigger to keep data consistency : Utility trigger « Trigger « Oracle PL/SQL Tutorial

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Oracle PL/SQL Tutorial » Trigger » Utility trigger 
28. 20. 1. Use trigger to keep data consistency
SQL>
SQL>
SQL> create table ord
  2          (
  3           order_no               integer         primary key
  4          ,empl_no                integer
  5          ,order_date             date not null
  6          ,total_order_price      number(7,2)
  7          ,deliver_date           date
  8          ,deliver_time           varchar2(7)
  9          ,payment_method         varchar2(2)
 10          ,emp_no                 number(3,0)
 11          ,deliver_name           varchar2(35)
 12          ,gift_message           varchar2(100)
 13           );

Table created.

SQL>
SQL>
SQL>
SQL> insert into ord(order_no,empl_no,order_date,total_order_price,deliver_date,deliver_time,payment_method,emp_no,deliver_name,gift_message)
  2  values(1,1,add_months(sysdate, -1)235.00'14-Feb-1999', '12 noon', 'CA',1, null, 'Gift for wife');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time ,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(2,1,add_months(sysdate, -2)50.98'14-feb-1999', '1 pm', 'CA',7'Rose', 'Happy Valentines Day to Mother');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(32,add_months(sysdate, -3)35.99'14-feb-1999', '1 pm', 'VS',2'Ruby', 'Happy Valentines Day to Mother');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(42,add_months(sysdate, -4)19.95'14-feb-1999', '5 pm', 'CA',2'Coy', 'Happy Valentines Day to You');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(79,add_months(sysdate, -7)35.95'21-jun-1999', '12 noon', 'VS', 2'Fill', 'Happy Birthday from Joe');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values (812, add_months(sysdate, -8)35.95'1-jan-2000', '12 noon', 'DI',3'Laura', 'Happy New Year''s from Lawrence');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values (912, add_months(sysdate, -9)75.95'2-jan-2000', '12 noon', 'CA',7'Sara', 'Happy Birthday from Lawrence' );

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(104, add_months(sysdate, -10)19.95, sysdate, '2:30 pm', 'VG',2'OK', 'Happy Valentines Day to You');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2  values(112, add_months(sysdate, -11)30.00, sysdate+2'1:30 pm', 'VG',2'Hi', 'Happy Birthday Day to You');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message)
  2  values(127, add_months(sysdate, -12)21.95, sysdate-2'3:30 pm', 'CA',2'Jack', 'Happy Birthday Day to You');

row created.

SQL>
SQL> insert into ord(order_no  ,empl_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message)
  2  values(137, add_months(sysdate, -1)21.95, sysdate, '3:30 pm', 'CA',2'Jay', 'Thanks for giving 100%!');

row created.

SQL>
SQL>
SQL>
SQL>
SQL> create table ord_item
  2          (
  3           order_no               integer
  4          ,product_id             integer
  5          ,quantity               number(4,0)
  6          ,item_price                 number(7,2)
  7        ,total_order_item_price   number(9,2)
  8          ,primary key (order_no ,product_id)
  9          );

Table created.

SQL>
SQL>
SQL>
SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(1,   2,  1023.00 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(21123.00 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(25110.50 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(28117.48 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(38135.99 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(47119.95 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(55110.95 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(68122.95 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(71615.00 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(75110.50 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(78110.45 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(88135.95 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(98165.45 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(95110.50 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(103119.95 );

row created.

SQL> insert into ord_item (order_no, product_id, quantity, item_pricevalues(118130.00);

row created.

SQL>
SQL>
SQL>
SQL>
SQL>
SQL> create or replace trigger tr_total_order_price
  2  after
  3  update of item_price or insert or delete
  4  on ord_item
  5  for each row
  6  declare
  7      v_change_in_price  number;
  8      v_order_no number;
  9  begin
 10  if inserting then
 11      v_change_in_price := :new.item_price * :new.quantity ;
 12      v_order_no := :new.order_no;
 13      dbms_output.put_line('inserting');
 14  elsif updating then
 15      v_change_in_price := (:new.item_price * :new.quantity(:old.item_price * :old.quantity;
 16      v_order_no := :old.order_no;
 17      dbms_output.put_line('updating');
 18  else
 19      v_change_in_price := (:old.item_price * :old.quantity)  * -1;
 20      v_order_no := :old.order_no;
 21      dbms_output.put_line('deleting');
 22  end if;
 23
 24  update ord
 25  set total_order_price = total_order_price + v_change_in_price
 26  where order_no = v_order_no;
 27  end;
 28  /

Trigger created.

SQL>
SQL> update ord_item set item_price = 25 where order_no = and product_id = ;

row updated.

SQL>
SQL>
SQL> drop table ord;

Table dropped.

SQL>
SQL> drop table ord_item;

Table dropped.

SQL>
28. 20. Utility trigger
28. 20. 1. Use trigger to keep data consistency
28. 20. 2. A trigger prevents updates after business hours
28. 20. 3. Records a error in the error logging table.
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