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Oracle PL/SQL – 嵌套循环

简述

PL/SQL 允许在另一个循环中使用一个循环。以下部分显示了一些示例来说明这个概念。
PL/SQL 中嵌套基本 LOOP 语句的语法如下:

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

PL/SQL 中嵌套 FOR LOOP 语句的语法如下:

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;

Pascal 中嵌套的 WHILE LOOP 语句的语法如下:

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

例子

以下程序使用嵌套的基本循环来查找从 2 到 100 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;
/

在 SQL 提示符下执行上述代码时,会产生以下结果 –

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.

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