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oraclegoto语句介绍

来源:互联网 作者:佚名 时间:2015-11-28 09:29
TheOraclePL/SQL GOTO statement is a sequential control structure available in Oracle. The GOTO statement immediately transfers program control (called branching) unconditionally to a named statement label or block label. The statement or

The Oracle PL/SQL GOTO statement is a sequential control structure available in Oracle. The GOTO statement immediately transfers program control (called "branching") unconditionally to a named statement label or block label. The statement or label name must be unique in the block.

属于plsql控制语句,用于程序控制非条件跳至指定标签<<???>>。不易控制和维护,慎用!

二 例子:

1、简单GOTO 语句,判断数字是否为质数:

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DECLARE

  p VARCHAR2(30);

  n PLS_INTEGER := 37; -- test any integer > 2 for prime

BEGIN

  FOR j IN 2 .. round(sqrt(n)) LOOP

    IF n MOD j = 0 THEN

      -- test for prime

      p := ' is not a prime number'; -- not a prime number

      GOTO print_now;

    END IF;

  END LOOP;

  p := ' is a prime number';

  <<print_now>>

  dbms_output.put_line(to_char(n) || p);

END;

/

2、使用null避免报错:

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DECLARE

  done BOOLEAN;

BEGIN

  FOR i IN 1 .. 50 LOOP

    IF done THEN

      GOTO end_loop;

    END IF;

    <<end_loop>> -- not allowed unless an executable statement follows

    NULL; -- add NULL statement to avoid error

  END LOOP; -- raises an error without the previous NULL

END;

/

3、使用goto分出一个环绕块:

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-- example with GOTO statement

DECLARE

  v_last_name VARCHAR2(25);

  v_emp_id    NUMBER(6) := 120;

BEGIN

  <<get_name>>

  SELECT last_name

  INTO v_last_name

  FROM employees

  WHERE employee_id = v_emp_id;

  BEGIN

    dbms_output.put_line(v_last_name);

    v_emp_id := v_emp_id + 5;

    IF v_emp_id < 120 THEN

      GOTO get_name; -- branch to enclosing block

    END IF;

  END;

END;

/

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