oracle的新发现for语句

今天为了解决一个查询结果想两次遍历的方法，去ORACLE官网文档中心 https://docs.oracle.com/en/database/oracle/，意外发现这个有意思的for语句。还是官方资料给力啊

遍历一个游标

DECLARE
  CURSOR c1 IS
    SELECT last_name, job_id FROM employees
    WHERE job_id LIKE '%CLERK%' AND manager_id > 120
    ORDER BY last_name;
BEGIN
  FOR item IN c1
  LOOP
    DBMS_OUTPUT.PUT_LINE
      ('Name = ' || item.last_name || ', Job = ' || item.job_id);
  END LOOP;
END;
/

遍历一个子查询

BEGIN
  FOR item IN (
    SELECT first_name || ' ' || last_name AS full_name,
           salary * 10                    AS dream_salary
    FROM employees
    WHERE ROWNUM <= 5
    ORDER BY dream_salary DESC, last_name ASC
  ) LOOP
    DBMS_OUTPUT.PUT_LINE
      (item.full_name || ' dreams of making ' || item.dream_salary);
  END LOOP;
END;
/

遍历列的列表

DECLARE
  TYPE empcurtyp IS REF CURSOR;
  TYPE namelist IS TABLE OF employees.last_name%TYPE;
  TYPE sallist IS TABLE OF employees.salary%TYPE;
  emp_cv  empcurtyp;
  names   namelist;
  sals    sallist;
BEGIN
  OPEN emp_cv FOR
    SELECT last_name, salary FROM employees
    WHERE job_id = 'SA_REP'
    ORDER BY salary DESC;

  FETCH emp_cv BULK COLLECT INTO names, sals;
  CLOSE emp_cv;
  -- loop through the names and sals collections
  FOR i IN names.FIRST .. names.LAST
  LOOP
    DBMS_OUTPUT.PUT_LINE
      ('Name = ' || names(i) || ', salary = ' || sals(i));
  END LOOP;
END;
/

FOR循环使用关键字REVERSE倒着来

BEGIN
  DBMS_OUTPUT.PUT_LINE ('upper_bound > lower_bound');

  FOR i IN REVERSE 1..3 LOOP
    DBMS_OUTPUT.PUT_LINE (i);
  END LOOP;

  DBMS_OUTPUT.PUT_LINE ('upper_bound = lower_bound');

  FOR i IN REVERSE 2..2 LOOP
    DBMS_OUTPUT.PUT_LINE (i);
  END LOOP;

  DBMS_OUTPUT.PUT_LINE ('upper_bound < lower_bound');

  FOR i IN REVERSE 3..1 LOOP
    DBMS_OUTPUT.PUT_LINE (i);
  END LOOP;
END;
/
 

更有意思的游标里可以包含游标对象

DECLARE
  TYPE emp_cur_typ IS REF CURSOR;

  emp_cur    emp_cur_typ;
  dept_name  departments.department_name%TYPE;
  emp_name   employees.last_name%TYPE;

  CURSOR c1 IS
    SELECT department_name,
      CURSOR ( SELECT e.last_name
                FROM employees e
                WHERE e.department_id = d.department_id
                ORDER BY e.last_name
              ) employees
    FROM departments d
    WHERE department_name LIKE 'A%'
    ORDER BY department_name;
BEGIN
  OPEN c1;
  LOOP  -- Process each row of query result set
    FETCH c1 INTO dept_name, emp_cur;
    EXIT WHEN c1%NOTFOUND;
    DBMS_OUTPUT.PUT_LINE('Department: ' || dept_name);

    LOOP -- Process each row of subquery result set
      FETCH emp_cur INTO emp_name;
      EXIT WHEN emp_cur%NOTFOUND;
      DBMS_OUTPUT.PUT_LINE('-- Employee: ' || emp_name);
    END LOOP;
  END LOOP;
  CLOSE c1;
END;
/

Exit还可以这样用

DECLARE
  s  PLS_INTEGER := 0;
  i  PLS_INTEGER := 0;
  j  PLS_INTEGER;
BEGIN
  <<outer_loop>>
  LOOP
    i := i + 1;
    j := 0;
    <<inner_loop>>
    LOOP
      j := j + 1;
      s := s + i * j; -- Sum several products
      EXIT inner_loop WHEN (j > 5);
      EXIT outer_loop WHEN ((i * j) > 15);
    END LOOP inner_loop;
  END LOOP outer_loop;
  DBMS_OUTPUT.PUT_LINE
    ('The sum of products equals: ' || TO_CHAR(s));
END;
/
 

continue也可以使用when

DECLARE
  x NUMBER := 0;
BEGIN
  LOOP -- After CONTINUE statement, control resumes here
    DBMS_OUTPUT.PUT_LINE ('Inside loop:  x = ' || TO_CHAR(x));
    x := x + 1;
    CONTINUE WHEN x < 3;
    DBMS_OUTPUT.PUT_LINE
      ('Inside loop, after CONTINUE:  x = ' || TO_CHAR(x));
    EXIT WHEN x = 5;
  END LOOP;
  DBMS_OUTPUT.PUT_LINE (' After loop:  x = ' || TO_CHAR(x));
END;
/
 

FOR循环中变量可以重名

BEGIN
  <<outer_loop>>
  FOR i IN 1..3 LOOP
    <<inner_loop>>
    FOR i IN 1..3 LOOP
      IF outer_loop.i = 2 THEN
        DBMS_OUTPUT.PUT_LINE
          ('outer: ' || TO_CHAR(outer_loop.i) || ' inner: '
           || TO_CHAR(inner_loop.i));
      END IF;
    END LOOP inner_loop;
  END LOOP outer_loop;
END;
/

跳转语句GOTO的使用

DECLARE
  p  VARCHAR2(30);
  n  PLS_INTEGER := 37;
BEGIN
  FOR j in 2..ROUND(SQRT(n)) LOOP
    IF n MOD j = 0 THEN
      p := ' is 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;
/
 

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;
    END IF;
  END;
END;
/
 

创建可以传参的游标

DECLARE
  CURSOR c1 (job VARCHAR2, max_wage NUMBER) IS
    SELECT * FROM employees
    WHERE job_id = job
    AND salary > max_wage;
BEGIN
  FOR person IN c1('ST_CLERK', 3000)
  LOOP
     -- process data record
    DBMS_OUTPUT.PUT_LINE (
      'Name = ' || person.last_name || ', salary = ' ||
      person.salary || ', Job Id = ' || person.job_id
    );
  END LOOP;
END;
/

两次遍历一个结果的最终解法

declare
  cursor c1 is
      select stockInfo from T_stock ORDER BY id;
BEGIN
  FOR item IN c1
  LOOP
    DBMS_OUTPUT.PUT_LINE
      ('首次输出 = ' || item.stockInfo);
  END LOOP;
  FOR item IN c1
  LOOP
    DBMS_OUTPUT.PUT_LINE
      ('二次访问 = ' || item.stockInfo);
  END LOOP;
END;