MySQL常见笔试题类型及解法总结

最近看了一下数据库方面的面试题，发现有些情况不常用的都忘了怎么解决了，所以在此做一个总结，方便之后复习。

先建一个这样的数据库表student_score表，结构及数据如下图所示：
在这里插入图片描述
创建表及插入数据的SQL脚本如下：

CREATE TABLE student_score (
  `pk_id` varchar(36) NOT NULL,
  `student_id` int(15) NOT NULL,
  `student_name` varchar(24) NOT NULL,
  `category` varchar(10) NOT NULL,
  `score` int(10) DEFAULT NULL,
  PRIMARY KEY (`pk_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO student_score 
(pk_id,student_id,student_name,category,score)
VALUES
('aabbcc','10011','张三','数学','56'),
('aabbcd','10011','张三','语文','88'),
('aabbdc','10011','张三','英语','67'),
('aabdcc','10012','李四','语文','67'),
('aadbcc','10012','李四','数学','88'),
('adbbcc','10012','李四','英语','30'),
('aabscc','10013','王五','数学','66'),
('afbbcc','10013','王五','英语','76'),
('vabbcc','10013','王五','语文','88'),
('aasdcc','10014','赵七','数学','88'),
('agbbcc','10014','赵七','英语','96'),
('agbbsa','10014','赵七','英语','96'),
('aubbcc','10014','赵七','语文','80'),
('adcdsd','10015','马六','数学','33'),
('dfasdv','10015','马六','英语','45'),
('dsdfgd','10015','马六','语文','55'),
('dsdfad','10015','马六','语文','55');

有了以上数据，就可以进行操作了，以下是一些常见题型，包含了基本操作和一些相对较复杂的操作：

#查询所有数据
SELECT
	*
FROM
	student_score;

#查询学生总数,不加临时表名会报错
SELECT
	count(1)
FROM
	(
		SELECT DISTINCT
			student_name
		FROM
			student_score
	) t1;

#查询姓名为张三的成绩
SELECT
	student_id,
	student_name,
	score
FROM
	student_score
WHERE
	student_name = '张三';

#查询所有学生的数学成绩
SELECT
	student_id,
	student_name,
	score
FROM
	student_score
WHERE
	category = '数学';

#查询张三的数学成绩
SELECT
	student_id,
	student_name,
	score
FROM
	student_score
WHERE
	student_name = '张三'
AND category = '数学';

#查询所有成绩存在不及格的学生的学号和姓名
SELECT DISTINCT
	student_id,
	student_name
FROM
	student_score
WHERE
	score < 60;

#查询所有成绩都及格的学生的学号和姓名
SELECT DISTINCT
	student_id,
	student_name
FROM
	student_score
WHERE
	student_name NOT IN (
		SELECT
			student_name
		FROM
			student_score
		WHERE
			score < 60
		GROUP BY
			student_name
	);

#查询成绩至少两门及格的学生的学号和姓名
SELECT DISTINCT
	student_id,
	student_name
FROM
	student_score
WHERE
	student_name NOT IN (
		SELECT
			student_name
		FROM
			student_score
		WHERE
			score < 60
		GROUP BY
			student_name
		HAVING
			count(category) > 1
	);
	
#或者：

SELECT
	student_id,
	student_name
FROM
	student_score
WHERE
	score >= 60
GROUP BY
	student_name
HAVING
	count(category) >= 2;

#查询成绩至少两门及格的学生的学号和姓名，以及显示出及格的科目
SELECT
	student_id,
	student_name,
	GROUP_CONCAT(category)
FROM
	student_score
WHERE
	score >= 60
GROUP BY
	student_name
HAVING
	count(category) >= 2;

#查找每门课都在80以上的学生的学号和姓名
SELECT DISTINCT
	student_id,
	student_name
FROM
	student_score
WHERE
	student_name NOT IN (
		SELECT DISTINCT
			student_name
		FROM
			student_score
		WHERE
			score < 80
	);

#删除除pk_id外其他其他数据都相同的冗余数据
DELETE
FROM
	student_score
WHERE
	pk_id NOT IN (
		SELECT
			*
		FROM
			(
				SELECT
					min(pk_id)
				FROM
					student_score
				GROUP BY
					student_id,
					student_name,
					score,
					category
			) t1
	) 
#找到分数大于80的最多的科目及人数
SELECT
	category,
	count
FROM
	(
		SELECT
			category,
			COUNT(category) AS count
		FROM
			(
				SELECT
					category
				FROM
					student_score
				WHERE
					score >= 80
			) t1
		GROUP BY
			category
	) t2
WHERE
	count = (
		SELECT
			max(count)
		FROM
			(
				SELECT
					category,
					COUNT(category) AS count
				FROM
					(
						SELECT
							category
						FROM
							student_score
						WHERE
							score >= 80
					) t1
				GROUP BY
					category
			) t2
	)

目前想到的就是这些，以后再遇到别的类型再添加，如果有读者看到有想补充的可以评论，我后期补上。

MySQL常见笔试题类型及解法总结

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