Introduction to pl/sql, very detailed notes

PL/SQL introduction , Very detailed notes

-- PL/SQL brief introduction :
1.PL/SQl It's process language PL And structured languages SQL Combined programming language 
2.PL/SQL The engine resides in Oracle Server 
3. The engine receives PL/SQL Block and compile it 

-- PL/SQL  block :
 It's the composition PL/SQL The basic unit of composition , Combine logically related declarations and statements 
PL/SQL It's divided into three parts , Declaration part , The executable part , And exception handling 
-- PL/SQL  grammar : 
[declare 
        Declaration part ]
[begin
        The executable part 
       ] 
 [exception
        Exception handling part    
 end
 ] 
/* PL/SQL Is a strongly typed programming language , All variables must be declared before they can be used ,  Variables are required in declare Partial declaration , There are the following provisions for variable names : 1. Variable names can be alphanumeric underscores $# Other components  2. All variable names should start with a letter , It can't be Oracle Keywords in  3. The length of the variable can only be 30 Characters  --  In order to improve the PL/SQL Readability , All variables use "v_ Variable name " Define  */
declare 
    v_name varchar2(20) :=' Who am I ?';
begin
 --  Output operation 
 dbms_output.put_line('pl/sql The output operation of ' || v_name); -- PL/SQL  Use... In string || Connect 
end;

--  Use into Assign values to variables 
declare 
   v_name varchar2(20);
begin 
  --  adopt SQL Statement and into Keyword assigns a value to a variable 
   select uname into v_name  from user_book where userid=9999;
   dbms_output.put_line(v_name); --  Print 
end;

-- %type The type of the specified field 
declare 
   v_name user_book.uname%type;
   v_id user_book.userid%type;
   begin
     --  Assign values to fields 
         select user_book.uname,user_book.userid into v_name,v_id 
                from user_book 
                where user_book.userid=9999;
  --  Output to see the results 
  dbms_output.put_line(v_id || v_name);
end;

-- %rowtype  Data representing the entire row in the table 
declare 
   v_row user_book%rowtype;
begin
  --  assignment 
  select * into v_row from user_book  where user_book.userid=9999; 
  --  Output the data in the row :  Note that at this time, all fields in the row must be written into the output statement manually , Otherwise, an error will be reported 
  dbms_output.put_line(v_row.uname||v_row.userid||v_row.urole );
end;

--  Conditional statements 
/* 1. if else  sentence : if  Conditions 1 then  Meet the conditions 1 The statement executed when  else  Conditions 2 then  Meet the conditions 2 The statement executed when  */

/* 2. case when  sentence : case when  Conditions 1 then  Meet the conditions 1 Code executed at  when  Conditions 2 then  Meet the conditions 2 Code executed at  when  Conditions 3 then  Meet the conditions 3 Code executed at  else  Code executed when none of the above conditions are met  end case; */

--  loop 
/* -- 1.exit when  Exit loop : loop  Statement block executed in a loop ; exit when Cycle end condition ;  Step statement ; end loop; */
declare 
      v_i int := 0; --  Declare variables 
begin
  loop
    dbms_output.put_line(v_i); --  Cyclic block :  Print v_i
    exit when v_i >= 10; --  The end condition 
    v_i := v_i+1; --  Step statement 
  end loop;
  end;

/* -- 2.while loop : while  Cycle end condition  loop  The loop body ;  Step statement ; end loop; */
declare 
      v_i int := 0; --  Declare variables 
begin
  while exit when v_i >= 10; --  The end condition 
  loop
    dbms_output.put_line(v_i); --  Cyclic block :  Print v_i
    v_i := v_i+1; --  Step statement 
  end loop;
  end;

/* -- 3.for in  loop : for  Circular index variable  in [recerse] -- reverse:  reverse   Lower limit of cycle area .. Loop area online  loop  Loop statement block ; end loop ; */

declare 
begin
  for i in  1..10  --  from 1 To 10  positive sequence 
    loop
    dbms_output.put_line(i); --  Print i
    end loop;
end; 

--  exception handling 
/* 1. Definition : Errors that occur when running exceptions are called exceptions  2. characteristic :  When something goes wrong , Statement will stop executing , The transfer of control to PL/SQL The exception handling part of the block  3. Three types of exceptions :  Predefined exceptions : When PL/SQL Procedural violation Oracle Implicitly raised when rules or system limits are exceeded ;  Users do not need to define ;  Non predefined exception : When PL/SQL Procedural violation Oracle Caused when rules or system limits are exceeded ;  Users need to define ;  User defined exception : The user is required to define , Explicitly raise ; */
--  Syntax of exception handlers :
   begin
      General code block ;
   exception 
     when  Abnormal conditions 1 Satisfy  then  Abnormal conditions 1 Code to execute when satisfied 
       when  Abnormal conditions 2 Satisfy  then  Abnormal conditions 2 Code to execute when satisfied 
          when others then  Code executed when none of them are satisfied 
   end;   

--  Common system exceptions : 
        --  Excessive data : to_many_rows
        --  The query data does not exist : no_data_found

declare 
   v_error exception;
   v_name user_book.uname%type;
 begin
   select uname into v_name from user_book where user_book.userid=100000; --  At this time userid It doesn't exist 
 end;
--  User defined exception 
-- -----------------------------------
declare 
   v_error exception;
   v_name user_book.uname%type;
 begin
   select uname into v_name from user_book where user_book.userid=100000; 
    if v_name = ' Zhang San ' then  --  If the condition is met, return v_error
      raise v_error;
      end if;
          exception 
            when v_error then  --  Triggered when this exception occurs 
             dbms_output.put_line(' It was Zhang San , Throw an exception to you ');
 end;