基础知识(1)

--if then  elsif then end if; 
declare 
 a number;
 b varchar2(10);
begin
  a := 2;
  if a=1 then 
   b :='a';
  elsif a=2 then
   b := 'b';
   else 
   b := 'c';
  end if;
Dbms_Output.put_line('b is '|| b);
end;
--case when 
declare 
a number;
b varchar2(10);
begin 
 a := 2;
case
when a=1 then b := 'a';
when a=2 then b := 'b';
when a=3 then b := 'c';
else
b := 'others';
end case;
dbms_output.put_line('b is '|| b);
end;

--loop end loop
declare 
x number;
begin
 x := 0;
 loop
 x := x+ 1;
 if x >=3 then 
 exit;
 end if;
 dbms_output.put_line('内:x='||x);
 end loop;
 dbms_output.put_line('外:x='||x);
 end;
 
 --exit when 方式
 declare 
 x number;
 begin
  x:= 0;
  loop
  x:=x+1;
  exit when x>=3;
  dbms_output.put_line('内:x='||x);
  end loop;
  dbms_output.put_line('外:x='||x);
 end;
 
 begin
 for i in reverse 1..5 loop
 dbms_output.put_line('i='||i);
 end loop;
 dbms_output.put_line('end of for loop');
 end;