PL/SQL嵌套循環(huán)

PL/SQL允許使用一個循環(huán)內(nèi)嵌套另一個循環(huán)。下面的內(nèi)容展示幾個例子來說明這個概念。

在PL/SQL嵌套基本LOOP語句的語法如下：

LOOP
   Sequence of statements1
   LOOP
      Sequence of statements2
   END LOOP;
END LOOP;

在PL/SQL 循環(huán)FOR語句嵌套的語法如下：

FOR counter1 IN initial_value1 .. final_value1 LOOP
   sequence_of_statements1
   FOR counter2 IN initial_value2 .. final_value2 LOOP
      sequence_of_statements2
   END LOOP;
END LOOP;

在Pascal嵌套WHILE 循環(huán)語句的語法如下：

WHILE condition1 LOOP
   sequence_of_statements1
   WHILE condition2 LOOP
      sequence_of_statements2
   END LOOP;
END LOOP;

示例:

下面的程序使用一個基本嵌套循環(huán)，找出2-100中的素數(shù)：

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;
/

當上述代碼在SQL提示符執(zhí)行時，它產(chǎn)生了以下結果：

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime

PL/SQL procedure successfully completed.