The use of database stored procedures and stored functions in Oracle

Stored procedures and stored functions refer to the subroutines stored in the database for all user programs to call, called stored procedures and stored functions.
The stored procedure has no return value. Stored functions have return values

  Create stored procedure
      Create stored procedures and stored functions with the CREATE PROCEDURE command.

      grammar:
create [or replace] PROCEDURE procedure name (parameter list)
AS
        PLSQL subroutine body;

  Stored procedure example: increase the salary by 10% on the basis of the original salary for the specified employee
 
/*
Increase the salary by 10% on the basis of the original salary for the designated employee, and print the salary before and after the salary
*/
SQL> create or replace procedure raiseSalary(empid in number)
    as
    pSal emp.sal%type;--Save the current salary of the employee
    begin
-- Query the employee's salary
    select sal into pSal from emp where empno=empid;
- Give the employee a salary increase
    update emp set sal = sal*1.1 where empno=empid;
--Print the salary before and after the salary increase
    dbms_output.put_line('Employee number:' || empid || 'Before salary increase
   ' || psal || 'After salary increase' || psal*1.1);
    end;
 1  /

Procedure created
--stored procedure call
--method one
SQL> set serveroutput on
SQL> exec raisesalary(7369);

Employee number: 7369 Before salary increase
800 880 after salary increase

Method Two
    set serveroutput on
begin
 raisesalary(7369);
end;
/

PL/SQL procedure successfully completed

 
      stored function
      A function is a named stored procedure that can take parameters and return a computed value. Functions and procedures are similar in structure, but must have a RETURN clause that returns the function value. The function specification specifies the function name, the type of the result value, and the parameter type.

     Syntax to create a stored function:

CREATE [OR REPLACE] FUNCTION function name (parameter list)
RETURN function value type
AS
PLSQL subroutine body;

 
Example: Query the annual income of an employee.
SQL> /**/
    /*
    Query the total income of an employee
    */
    create or replace function queryEmpSalary(empid in number)
    return number
   as
    pSal number; --Define a variable to hold the employee's salary
    pComm number; -- define a variable to hold the employee's bonus
   begin
   select sal,comm into psal,pcomm from emp where empno = empid;
   return psal*12+nvl(pcomm,0);
   end;
   /

Function created

   l function call

SQL> declare
    v_sal number;
    begin
    v_sal:=queryEmpSalary(7934);
    dbms_output.put_line('salary is:'|| v_sal);
    end;
    /

salary is:15600

PL/SQL procedure successfully completed

SQL> begin
    dbms_output.put_line('salary is:'|| queryEmpSalary(7934));
    end;
    /

salary is:15600

PL/SQL procedure successfully completed

 
       trigger
       A database trigger is a stored PL/SQL program associated with a table. Whenever a specific data manipulation statement (Insert, update, delete) is issued on the specified table, Oracle automatically executes the sequence of statements defined in the trigger.

       type of trigger
         Statement level triggers
        Executes once before or after the specified action statement, regardless of how many rows the statement affects.

         Row-level triggers (FOR EACH ROW)
        Every record that the trigger statement acts on is triggered. Use old and new pseudo-record variables in row-level triggers to identify the state of a value.

      Create a trigger
CREATE [or REPLACE] TRIGGER trigger name
   {BEFORE | AFTER}
   {DELETE | INSERT | UPDATE [OF列名]}
   ON table name
   [FOR EACH ROW [WHEN(条件) ] ]
   PLSQL block

       Example 1: Restrict inserting data into the database during non-working hours
SQL> create or replace
    trigger securityEmp
    before insert on emp
    declare
    begin
    if to_char(sysdate,'day')in('Thursday','Saturday','Sunday')
    or to_number(to_char(sysdate,'hh24'))not between 8 and 18 then
    raise_application_error(-20001, 'Cannot insert data during non-working hours.');
    end if;
   end;
   /

Trigger created

Trigger Statement and Pseudo Record Variable Value
trigger statement
:old
:new
Insert
All fields are empty (null)
data to be inserted
Update
Update the previous value of the row
updated value
delete
delete the previous value of the row
All fields are empty (null)
Example 2: Confirm data (check that the modified value of sal in the emp table is not lower than the original value)
SQL> create or replace trigger checkSal
    before update of sal on emp
    for each row
    declare
    begin
    if :new.sal<:old.sal then
    raise_application_error(-20001, 'The salary after the update is smaller than before the update');
    end if;
    end;
   /

Trigger created
Result after running:
SQL> update emp set sal=260 where empno=7499;

update emp set sal=260 where empno=7499

ORA-20001: updated salary is less than before update
ORA-06512: 在 "SCOTT.CHECKSAL", line 4
ORA-04088: error during execution of trigger 'SCOTT.CHECKSAL'

       Trigger Summary
      Triggers can be used for
• Data confirmation
• Implement complex security checks
• Do auditing, track data operations done on tables, etc.

      Query triggers, procedures, and functions
•         Select * from user_triggers;
•         Select * from user_source;