一 定义：
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_idNUMBER(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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dylan presents.
