mysql游标嵌套循环

最近在mysql开发过程中用到了游标的嵌套循环,下面列举了3种嵌套循环(loop-loop,loop-while,loop-repeat).

程序用到的表和数据

CREATE TABLE tb_dic_class (
  class_id int(11) DEFAULT NULL,
  class_name varchar(20) DEFAULT NULL,
  createtime datetime DEFAULT 'CURRENT_TIMESTAMP',
  modifytime datetime DEFAULT 'CURRENT_TIMESTAMP'
)
ENGINE = INNODB
AVG_ROW_LENGTH = 5461
CHARACTER SET utf8
COLLATE utf8_general_ci;

CREATE TABLE tb_students (
  id int(11) NOT NULL,
  student_name varchar(30) DEFAULT NULL,
  class_id int(11) DEFAULT NULL,
  createtime datetime DEFAULT 'CURRENT_TIMESTAMP',
  modifytime datetime DEFAULT 'CURRENT_TIMESTAMP',
  PRIMARY KEY (id)
)
ENGINE = INNODB
AVG_ROW_LENGTH = 5461
CHARACTER SET utf8
COLLATE utf8_general_ci;

INSERT INTO tb_dic_class(class_id, class_name, createtime, modifytime) VALUES
(1, '一班', now(), now());
INSERT INTO tb_dic_class(class_id, class_name, createtime, modifytime) VALUES
(2, '二班', now(), now());
INSERT INTO tb_dic_class(class_id, class_name, createtime, modifytime) VALUES
(3, '三班', now(), now());

SET NAMES 'utf8';
INSERT INTO tb_students(id, student_name, class_id, createtime, modifytime) VALUES
(10, '张三', 1, now(), now());
INSERT INTO tb_students(id, student_name, class_id, createtime, modifytime) VALUES
(20, '李四', 1, now(), now());
INSERT INTO tb_students(id, student_name, class_id, createtime, modifytime) VALUES
(30, '王五', 3, now(), now());

1.loop-loop嵌套

CREATE PROCEDURE hxl.sp_loop_loop()
BEGIN
  DECLARE l_class_id int;
  DECLARE l_class_name varchar(20);
  DECLARE l_student_id int;
  DECLARE l_student_name varchar(20);
  DECLARE done int;

  DECLARE cur_out CURSOR FOR
  SELECT
    class_id,class_name
  FROM tb_dic_class;

  DECLARE cur_inner CURSOR FOR
  SELECT
    ID,
    student_name
  FROM tb_students
  WHERE class_id = l_class_id;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
  OPEN cur_out;
out_loop:
LOOP
  FETCH cur_out INTO l_class_id,l_class_name;

  IF done = 1 THEN
    LEAVE out_loop;
  END IF;
 
  open cur_inner;
 
  inner_loop:LOOP
    FETCH cur_inner INTO l_student_id,l_student_name;
    IF done = 1 THEN
       LEAVE inner_loop;
     end IF;
     SET @output_string= CONCAT('班级编码:',l_class_id,',班级名称:',l_class_name,',学生编号:',l_student_id,',学生名称:',l_student_name);
     SELECT @output_string;     
  end LOOP inner_loop;
  CLOSE cur_inner;
  SET done=0;

END LOOP out_loop;
  CLOSE cur_out;
END


2.loop-while嵌套

CREATE PROCEDURE sp_loop_while()
BEGIN DECLARE l_class_id     INT;
  DECLARE l_class_name   VARCHAR(20);
  DECLARE l_student_id   INT;
  DECLARE l_student_name VARCHAR(20);
  DECLARE done           INT;

  DECLARE cur_out CURSOR FOR
  SELECT class_id
       , class_name
  FROM
    tb_dic_class;

  DECLARE cur_inner CURSOR FOR
  SELECT ID
       , student_name
  FROM
    tb_students
  WHERE
    class_id = l_class_id;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

  OPEN cur_out;

out_loop:
LOOP
FETCH cur_out INTO l_class_id, l_class_name;

  IF done = 1 THEN
    LEAVE out_loop;
  END IF;

  OPEN cur_inner;

 
  SET done = 0; /* 内层循环控制*/
 
  FETCH cur_inner INTO l_student_id, l_student_name;
 
  WHILE done <> 1
  DO

    SET @output_string = concat('班级编码:', l_class_id, ',班级名称:', l_class_name, ',学生编号:', l_student_id, ',学生名称:', l_student_name);
    SELECT @output_string;
    FETCH cur_inner INTO l_student_id, l_student_name;
  END WHILE;

  CLOSE cur_inner;

  SET done = 0; /* 外层循环控制*/

END LOOP out_loop;
  CLOSE cur_out;
END

3.loop-repeat嵌套

CREATE PROCEDURE sp_loop_repeat()
BEGIN DECLARE l_class_id     INT;
  DECLARE l_class_name   VARCHAR(20);
  DECLARE l_student_id   INT;
  DECLARE l_student_name VARCHAR(20);
  DECLARE done           INT;

  DECLARE cur_out CURSOR FOR
  SELECT class_id
       , class_name
  FROM
    tb_dic_class;

  DECLARE cur_inner CURSOR FOR
  SELECT ID
       , student_name
  FROM
    tb_students
  WHERE
    class_id = l_class_id;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

  OPEN cur_out;

out_loop:
LOOP
FETCH cur_out INTO l_class_id, l_class_name;

  IF done = 1 THEN
    LEAVE out_loop;
  END IF;

  OPEN cur_inner;

  SET done = 0;
  REPEAT
    FETCH cur_inner INTO l_student_id, l_student_name;
   
    if done <> 1 then
     SET @output_string = concat('班级编码:', l_class_id, ',班级名称:', l_class_name, ',学生编号:', l_student_id, ',学生名称:', l_student_name);
     SELECT @output_string;        
    end if;

  UNTIL done
  END REPEAT;
  CLOSE cur_inner;

  SET done = 0; /* 外层循环控制*/

END LOOP out_loop;
  CLOSE cur_out;
END

 -- The End --