94 lines
2.7 KiB
MySQL
94 lines
2.7 KiB
MySQL
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CREATE TABLE students_241020 (
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id INT PRIMARY KEY AUTO_INCREMENT,
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name VARCHAR(100) NOT NULL,
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age INT NOT NULL,
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class VARCHAR(50) NOT NULL,
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score1 DECIMAL(5, 2) NOT NULL, -- 数学成绩
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score2 DECIMAL(5, 2) NOT NULL, -- 英语成绩
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score3 DECIMAL(5, 2) NOT NULL -- 语文成绩
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);
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INSERT INTO students_241020 (name, age, class, score1, score2, score3) VALUES
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('张三', 18, '高三1班', 90.50, 85.00, 92.00),
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('李四', 17, '高三2班', 88.00, 90.50, 87.00),
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('王五', 18, '高三1班', 92.00, 88.00, 89.00),
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('赵六', 17, '高三2班', 85.00, 92.00, 90.50),
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('孙七', 18, '高三1班', 87.00, 89.00, 91.00),
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('周八', 17, '高三2班', 90.00, 87.00, 88.00),
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('吴九', 18, '高三1班', 89.00, 91.00, 86.00),
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('郑十', 17, '高三2班', 91.00, 86.00, 87.00);
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# 获取每个班级的三科总分高于平均分（所有同学）的同学数量，并按照数量大小获取排名前三的班级，写出SQL语句
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SELECT
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tmp1.class, -- 选择班级字段
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count( tmp1.id ) AS `count` -- 统计每个班级的学生数
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FROM
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(
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-- 子查询，计算每个学生的总分
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SELECT s1.id, s1.class, s1.score1 + s1.score2 + s1.score3 AS `sum`
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FROM students_241020 s1
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) tmp1
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WHERE
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-- 条件判断，筛选出总分高于平均分的记录
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sum > (
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SELECT AVG( s.score1 + s.score2 + s.score3 )
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FROM students_241020 s
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)
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GROUP BY
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tmp1.class -- 按班级分组
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ORDER BY
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count DESC -- 按学生数降序排列
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LIMIT 3; -- 限制结果返回前三条记录
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SELECT
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tmp1.class, -- 选择班级字段
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count( tmp1.id ) AS `count` -- 统计每个班级的学生数
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FROM
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students_241020 tmp1
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WHERE
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-- 条件判断，筛选出总分高于平均分的记录
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tmp1.score1 + tmp1.score2 + tmp1.score3 > (
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SELECT AVG( s.score1 + s.score2 + s.score3 )
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FROM students_241020 s
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)
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GROUP BY
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tmp1.class -- 按班级分组
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ORDER BY
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count DESC -- 按学生数降序排列
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LIMIT 3; -- 限制结果返回前三条记录
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-- 使用临时表
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-- 计算平均分
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WITH avg_score AS (
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SELECT AVG(score1 + score2 + score3) AS avg_sum
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FROM students_241020
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),
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-- 子查询，计算每个学生的总分
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student_scores AS (
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SELECT id, class, score1 + score2 + score3 AS `sum`
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FROM students_241020
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)
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-- 查询总分高于平均分的班级及其学生数
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SELECT
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class, -- 选择班级字段
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COUNT(id) AS `count` -- 统计每个班级的学生数
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FROM
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student_scores
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WHERE
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`sum` > (SELECT avg_sum FROM avg_score)
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GROUP BY
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class -- 按班级分组
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ORDER BY
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`count` DESC -- 按学生数降序排列
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LIMIT 3; -- 限制结果返回前三条记录
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