PL/SQL - 巢狀迴圈

PL/SQL 允許在一個迴圈內使用另一個迴圈。下面的部分展示了幾個示例來闡釋該概念。

PL/SQL 中巢狀基本 LOOP 語句的語法如下所示 −

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

PL/SQL 中巢狀 FOR LOOP 語句的語法如下所示 −

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;

Pascal 中巢狀 WHILE LOOP 語句的語法如下所示 −

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

示例

下面的程式使用一個巢狀基本迴圈來找出 2 到 100 之間的質數 −

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; 
/

當在 SQL 提示符下執行上述程式碼時，它會產生以下結果 −

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.