Oracle triggers

Oracle trigger

Trigger application scenarios

Create trigger

create trigger saynewemp
after insert 
on emp
declare
  begin 
      dbms_output.put_line(" Successful insertion of new employees ");
  end;

grammar

type

• Statement level triggers

Execute once before or after the operation of the specified action statement , No matter how many lines this statement affects .

• Line level triggers

Every record that triggers a statement is triggered . Use... In row level triggers ：old and ：new Pseudo record variables , Identify the status of the value .

application

Application scenarios 1: Implement complex security checks （ It is forbidden to insert new employees during non working hours ）

/*
1.  Over the weekend ： to_char(sysdate,'day') in (' Saturday , Sunday ')
2.  Before going to work , After work  to_number( to_char(sysdate,'hh24')) not beween 9 and 18
*/

create or replace trigger securityemp
before insert 
on emp
begin 
if to_char(sysdate,'day') in (' Saturday ',' Sunday ') or 
to_number(to_char(sysdate,'hh24')) not between 9 and 18 then 

-- It is forbidden to insert new employees 
raise_application_error(-20001,' It is forbidden to insert new employees during non working hours ');

end if;

end;

Application scenarios 2： Pay rise cannot be less and less

/*
:old  and  :new  Represents the same record 
：old  Indicates before the operation of this line , The value of this line 
: new  Indicates that after the operation of this line , The value of this line 
*/

create or replace trigger checksalary
before update
on emp
for each row
begin 
-- if  The salary after the increase  <  Salary before increase  then
if :new.sal < :old.sal then
raise_application_error(-20002,' The salary after the rise cannot be less than the salary before the rise , The salary after the increase ：'|| :new.sal || ' Salary before increase :' :old.sal );
end if;

end;

Application scenarios 3： When the salary increases more than 6000 Block time , Audit the employee's information

create or replace trigger do_auid_emp_salary
after update
on emp
for each row
begin
   -- When the salary is higher than 6000, Insert audit information 
   if :new.sal > 6000 then 
   insert into audit_info values(:new.empno || '' ||:new.ename|| ''  ||:new.sal);
   end if;
end;

Application scenarios 4： Database backup and synchronization

create or replace trigger sync_salary
after update
on emp
for each row
begin
-- When the master table is updated . Update the backup table by yourself 
update emp_back set sal=:new.sal where empno=:new.empno;
end;
/

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