----PL/SQL基本循环语句  LOOP

DECLARE

   x number := 10;

BEGIN

   LOOP

      dbms_output.put_line(x);

      x := x + 10;

      IF x > 50 THEN

         exit;

      END IF;

   END LOOP;

   -- after exit, control resumes here

   dbms_output.put_line('After Exit x is: ' || x);

END; 

-- 可以用 exit when 代替 exit

DECLARE

   x number := 10;

BEGIN

   LOOP

          exit WHEN x > 50;

      dbms_output.put_line(x);

      x := x + 10; 

   END LOOP;

   -- after exit, control resumes here

   dbms_output.put_line('After Exit x is: ' || x);

END; 

---- while...loop

DECLARE

   a number(2) := 10;

BEGIN

   WHILE a < 20 LOOP

      dbms_output.put_line('value of a: ' || a);

      a := a + 2;  --增量可以随意

   END LOOP;

END; 

----for...loop 注意：增量只能是1

DECLARE

   a number(2);

BEGIN

   FOR a in 10 .. 20 LOOP

      dbms_output.put_line('value of a: ' || a);

  END LOOP;

END;

---- 反转FOR LOOP语句

DECLARE

   a number(2) ;

BEGIN

   FOR a IN REVERSE 10 .. 20 LOOP

      dbms_output.put_line('value of a: ' || a);

   END LOOP;

END; 

-- 嵌套循环   求出2到100之间的素数

DECLARE

   i number(3);

   j number(3);

BEGIN

   i := 2;

   LOOP

      j:= 2;

      LOOP

         exit WHEN ((mod(i, j) = 0) or (j = i));

         j := j +1;

      END LOOP;

   IF (j = i ) THEN

      dbms_output.put_line(i || ' is prime');

   END IF;

   i := i + 1;

   exit WHEN i = 50;

   END LOOP;

END;

-- 标记循环

DECLARE

   i number(1);

   j number(1);

BEGIN

   << outer_loop >>

   FOR i IN 1..3 LOOP

      << inner_loop >>

      FOR j IN 1..3 LOOP

         dbms_output.put_line('i is: '|| i || ' and j is: ' || j);

      END loop inner_loop;

   END loop outer_loop;

END; 

--循环控制语句：continue

DECLARE

   a number(2) := 10;

BEGIN

   -- while loop execution

   WHILE a < 20 LOOP

      dbms_output.put_line ('value of a: ' || a);

      a := a + 1;

      IF a = 15 THEN

         -- skip the loop using the CONTINUE statement

         a := a + 1;

         CONTINUE; -- 之后的代码跳过，回到条件开始重新迭代

      END IF;

   END LOOP;

END;

-- 循环控制语句：goto  不建议使用

DECLARE

   a number(2) := 10;

BEGIN

   <<loopstart>>

   -- while loop execution

   WHILE a < 20 LOOP

   dbms_output.put_line ('value of a: ' || a);

      a := a + 1;

      IF a = 15 THEN

         a := a + 1;

         GOTO loopstart;

      END IF;

   END LOOP;

END;