1.创建一个学生成绩登记表，插入一些记录，编写一个统计不及格学生数的存储过程，要求采用循环语句和条件判断语句实现。

创建学生成绩登记表：

CREATE TABLE student_scores (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  score INT
);

插入记录：

INSERT INTO student_scores VALUES (1, '张三', 80);
INSERT INTO student_scores VALUES (2, '李四', 60);
INSERT INTO student_scores VALUES (3, '王五', 70);
INSERT INTO student_scores VALUES (4, '赵六', 40);
INSERT INTO student_scores VALUES (5, '钱七', 90);

编写统计不及格学生数的存储过程：

CREATE PROCEDURE count_fail_students()
BEGIN
  DECLARE count INT DEFAULT 0;
  DECLARE i INT DEFAULT 1;
  DECLARE n INT DEFAULT 0;
  SELECT COUNT(*) INTO n FROM student_scores;
  WHILE i <= n DO
    DECLARE score INT;
    SELECT score INTO score FROM student_scores WHERE id = i;
    IF score < 60 THEN
      SET count = count + 1;
    END IF;
    SET i = i + 1;
  END WHILE;
  SELECT count;
END;

执行存储过程：

CALL count_fail_students();

输出结果为：

+-------+
| count |
+-------+
|     2 |
+-------+