What is PL/SQL
PL/SQL is a procedural SQL language (Procedural Language/SQL). PL/SQL is an extension of the Oracle database to SQL statements. The use of ordinary SQL statements adds the characteristics of programming languages, so PL/SQL organizes data operations and query statements in procedural units of PL/SQL code, and realizes complex functions or calculations through logical judgment, looping and other operations. programming language.
PL/SQL syntax
1）hello,world
--print Hello World
declare
--Description section
begin
-- program part
dbms_output.put_line('Hello World'); -- dbms_output is equivalent to a class in java
end;
/
2) Define the variable type
- reference variable
--reference variable: query and print the name and salary of 7839 declare --Define variables to hold name and salary --pename varchar2(20); -- Method 1 of declaring the variable type: directly define the type of the variable --psal number; penname emp.ename%type; -- way of declaring variable type 2 (reference variable): the same type as the ename column in the emp table psal emp.sal%type; begin -- Get 7839's name and salary select ename,sal into penname,psal from emp where empno=7839; -- use into to assign values to variables --Print dbms_output.put_line(pename||''s salary is'||psal); -- || is the string concatenation in Oracle end; /
- record variable
--Record variable: query and print the name and salary of 7839 declare --Define a record variable: representing a row in the emp table emp_rec emp%rowtype; begin select * into emp_rec from emp where empno=7839; dbms_output.put_line(emp_rec.ename||''s salary is'||emp_rec.sal); end; /
3) if statement
-- Determine the number entered by the user from the keyboard
--accept keyboard input
--Variable num: is an address value where the entered value is stored
accept num prompt 'Please enter a number';
declare
--Define a variable to hold the entered number
pnum number := #
begin
if pnum = 0 then dbms_output.put_line('you entered 0');
elsif pnum = 1 then dbms_output.put_line('you entered 1');
elsif pnum = 2 then dbms_output.put_line('you entered 2');
else dbms_output.put_line('other numbers');
end if;
end;
/
4) Loop
-- print 1~10
declare
-- define variables
pnum number := 1;
begin
loop
-- exit condition
exit when pnum > 10;
--Print
dbms_output.put_line(pnum);
--plus one
pnum := pnum + 1
end loop;
end;
/
5) Cursor
-- Query and print employee's name and salary
/*
Attributes of the cursor: %isopen (whether to open) %rowcount (the number of rows affected)
%found (whether there is a value) %notfound (whether there is no value)
*/
declare
--Define cursor (cursor)
cursor cemp is select ename,sal from emp;
pename emp.ename%type;
psal emp.sal%type;
begin
-- open cursor
open cemp;
loop
-- get current record
fetch cemp into pename,psal;
--exit when no record is retrieved;
exit when cemp%notfound;
dbms_output.put_line(pename||''s salary is'||psal);
end loop;
--close cursor
close cemp;
end;
/
Example: Raising wages for employees
-- Raise wages for employees, president 1000, manager 800, other 400
declare
-- define cursor
cursor cemp is select empno,job from emp;
pempno emp.empno%type;
pjob emp.job%type;
begin
-- open cursor
open cemp;
loop
-- take an employee
fetch cemp into pempno,pjob;
exit when cemp%notfound;
-- Judging position
if pjob = 'PRESIDENT' then update emp set sal=sal+1000 where empno=pempno;
elsif pjob = 'MANAGER' then update emp set sal=sal+800 where empno=pempno;
else update emp set sal=sal+400 where empno=pempno;
end if;
end loop;
--close cursor
close cemp;
--commit----> why?: Transaction ACID
commit;
dbms_output.put_line('完成');
end;
/
- Cursor with parameters
-- Query the names of employees in a department
declare
--form parameter
cursor cemp(dno number) is select ename from emp where deptno=dno;
pename emp.ename%type;
begin
--Arguments
open cemp(20);
loop
fetch cemp into pename;
exit when cemp%notfound;
dbms_output.put_line(pename);
end loop;
close cemp;
end;
/
6) Exception (exception)
- System exception
-- divide by 0
declare
pnum number;
begin
pnum := 1/0;
exception
when zero_divide then dbms_output.put_line('1:0 cannot be used as a denominator');
dbms_output.put_line('2:0 cannot be used as a denominator');
when value_error then dbms_output.put_line('arithmetic or conversion error');
when others then dbms_output.put_line('其他例外');
end;
/
- custom exception
-- Query employees in department 50 (department 50 does not exist)
declare
cursor cemp is select ename from emp where deptno=50;
pename emp.ename%type;
-- custom exception
no_emp_found exception;
begin
open cemp;
-- get the first record
fetch cemp into pename;
if cemp%notfound then
-- throw an exception, use raise
raise no_emp_found;
end if;
--Process: pmon process (proccesss monitor)
close cemp;
exception
when no_emp_found then dbms_output.put_line('employee not found');
when others then dbms_output.put_line('其他例外');
end;
/
Example 1: Count the number of employees hired each year (using PL/SQL)
/*
1. SQL statement
select to_char(hiredate,'yyyy') from emp;
---> Collection ---> Cursor ---> Loop ---> Exit: notfound
2. Variables: (*) how to get the initial value (*) in the end
Number of people hired each year
count80 number := 0;
count81 number := 0;
count82 number := 0;
count87 number := 0;
*/
declare
-- define cursor
cursor cemp is select to_char(hiredate,'yyyy') from emp;
phiredate varchar2(4);
- Number of people hired each year
count80 number := 0;
count81 number := 0;
count82 number := 0;
count87 number := 0;
begin
-- open cursor
open cemp;
loop
-- Take an employee's entry year
fetch cemp into phiredate;
exit when cemp%notfound;
--Determine what year it is
if phiredate = '1980' then count80:=count80+1;
elsif phiredate = '1981' then count81:=count81+1;
elsif phiredate = '1982' then count82:=count82+1;
else count87:=count87+1;
end if;
end loop;
--close cursor
close cemp;
--output
dbms_output.put_line('Total:'||(count80+count81+count82+count87));
dbms_output.put_line('1980:'|| count80);
dbms_output.put_line('1981:'|| count81);
dbms_output.put_line('1982:'|| count82);
dbms_output.put_line('1987:'|| count87);
end;
/
Example 2: Raise wages for employees. The person with the lowest total salary starts to increase. No one has a 10% increase, but the total salary does not exceed 10,000 yuan. Please calculate the number of people with long wages and the total wages after long wages.
/*
1. SQL statement
selet empno,sal from emp order by sal;
---> cursor ---> loop ---> exit: 1. total > 5w 2. notfound
2. Variables: (*) how to get the initial value (*) in the end
Number of people who have raised wages: countEmp number := 0;
The total salary after the increase: salTotal number;
(1)select sum(sal) into salTotal from emp;
(2) After the rise = before the rise + sal *0.1
Exercise: Number of people: 8 Total: 50205.325
*/
declare
cursor cemp is select empno,sal from emp order by sal;
pempno emp.empno%type;
psal emp.sal%type;
--The number of people with salary increase:
countEmp number := 0;
--The total salary after the increase:
salTotal number;
begin
-- Get the initial value of the total salary
select sum(sal) into salTotal from emp;
open cemp;
loop
-- 1. Total >5w
exit when salTotal > 50000;
-- take an employee
fetch cemp into pempno,psal;
--2. notfound
exit when cemp%notfound;
--rise salary
update emp set sal=sal*1.1 where empno=pempno;
--Number +1
countEmp := countEmp +1;
--After the rise = before the rise + sal *0.1
salTotal: = salTotal + psal * 0.1;
end loop;
close cemp;
commit;
dbms_output.put_line('Number: '||countEmp||' Total: '||salTotal);
end;
/
Example 3:
/*
1. SQL statement
Dept: select deptno from dept; ---> cursor
Salary of employees in a department: select sal from emp where deptno=?? ---> cursor with parameters
2. Variables: (*) how to get the initial value (*) in the end
Number of people in each segment
count1 number; count2 number; count3 number;
Department's gross salary
salTotal number: = 0;
(1)select sum(sal) into salTotal from emp where deptno=??
(2) Accumulation
*/
declare
--Department
cursor cdept is select deptno from dept;
pdeptno dept.deptno%type;
-- Salary of employees in the department
cursor cemp(dno number) is select sal from emp where deptno=dno;
psal emp.sal%type;
-- the number of people in each segment
count1 number; count2 number; count3 number;
--Department's total salary
salTotal number: = 0;
begin
--Department
open cdept;
loop
-- take a department
fetch cdept into pdeptno;
exit when cdept%notfound;
--initialization
count1:=0; count2:=0; count3:=0;
--Get the total salary of the department
select sum(sal) into salTotal from emp where deptno=pdeptno;
--Take the salary of middle employees in the department
open cemp(pdeptno);
loop
-- Take an employee's salary
fetch cemp into psal;
exit when cemp%notfound;
--judge
if psal < 3000 then count1:=count1+1;
elsif psal >=3000 and psal<6000 then count2:=count2+1;
else count3:=count3+1;
end if;
end loop;
close cemp;
--save results
insert into msg values(pdeptno,count1,count2,count3,nvl(saltotal,0));
end loop;
close cdept;
commit;
dbms_output.put_line('完成');
end;
/