Check the result of count aggregation function and then raise exception : raise_application_error « PL SQL Programming « Oracle PL/SQL Tutorial

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2. PL SQL Programming
3. raise_application_error

SQL>
SQL> create table ord(
  2           order_no               integer          primary key
  3          ,cust_no                integer
  4          ,order_date             date not null
  5          ,total_order_price      number(7,2)
  6          ,deliver_date           date
  7          ,deliver_time           varchar2(7)
  8          ,payment_method         varchar2(2)
  9          ,emp_no                 number(3,0)
 10          ,deliver_name           varchar2(35)
 11          ,gift_message           varchar2(100)
 12  );

Table created.

SQL>
SQL>
SQL> insert into ord(order_no,cust_no,order_date,total_order_price,deliver_date,deliver_time,payment_method,emp_no,deliver_name,gift_message)
  2           values(1,1,'14-Feb-2002', 23.00, '14-Feb-2002', '12 noon', 'CA',1, null, 'Gift for wife');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time ,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(2,1,'14-Feb-2003', 510.98, '14-feb-2003', '5 pm', 'NY',7, 'Rose Ted', 'Happy Valentines Day to Mother');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(3, 2,'14-Feb-2004', 315.99, '14-feb-2004', '3 pm', 'VS',2, 'Ani Forest', 'Happy Valentines Day to Father');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(4, 2,'14-Feb-1999', 191.95, '14-feb-1999', '2 pm', 'NJ',2, 'O. John', 'Happy Valentines Day');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message    )
  2           values(5, 6,'4-mar-2002', 101.95, '5-mar-2002', '2:30 pm', 'MO'    , 2, 'Cora', 'Happy Birthday from John');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(6, 9,'7-apr-2003', 221.95, '7-apr-2003', '3 pm', 'MA', 2, 'Sake Keith', 'Happy Birthday from Joe' );

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(7, 9,'20-jun-2004', 315.95, '21-jun-2004', '12 noon', 'BC', 2, 'Jessica Li', 'Happy Birthday from Jessica');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values (8, 12, '31-dec-1999', 135.95, '1-jan-2000', '12 noon', 'DI',   3, 'Larry', 'Happy New Year from Lawrence');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values (9, 12, '26-dec-2003', 715.95, '2-jan-2004', '12 noon', 'SK',7, 'Did', 'Happy Birthday from Nancy' );

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(10, 4, sysdate-1, 119.95, sysdate+2, '6:30 pm', 'VG',2, 'P. Jing', 'Happy Valentines Day to Jason');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message )
  2           values(11, 2, sysdate, 310.00, sysdate+2, '3:30 pm', 'DC',2, 'C. Late', 'Happy Birthday Day to Jack');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message)
  2           values(12, 7, sysdate-3, 121.95, sysdate-2, '1:30 pm', 'AC',2, 'W. Last', 'Happy Birthday Day to You');

1 row created.

SQL> insert into ord(order_no  ,cust_no ,order_date ,total_order_price ,deliver_date ,deliver_time,payment_method ,emp_no,deliver_name ,gift_message)
  2           values(13, 7, sysdate, 211.95, sysdate-4, '4:30 pm', 'CA',2, 'J. Bond', 'Thanks for hard working');

1 row created.

SQL>
SQL> create or replace procedure delete_cust
  2  (p_Cust_no in number)
  3  as
  4    l_count number;
  5
  6  begin
  7
  8     select count(*) into l_count
  9        from ord
 10        where cust_no = p_cust_no;
 11     if l_count != 0 then
 12       raise_application_error(-20000, 'cannot delete active cust');
 13     end if;
 14  end;
 15  /

Procedure created.

SQL> show errors
No errors.
SQL>
SQL> EXEC delete_cust(13);

PL/SQL procedure successfully completed.

SQL>
SQL> drop table ord;

Table dropped.

SQL>
SQL>