作业要求：根据要求完成单表,多表及分类汇总排序查
单表：
```sql
CREATE TABLE students (
id INT PRIMARY KEY,
name VARCHAR(50),
age INT,
score FLOAT
);
```
插入数据：
```sql
INSERT INTO students (id, name, age, score) VALUES
(1, '张三', 18, 90.5),
(2, '李四', 19, 85.0),
(3, '王五', 20, 78.5),
(4, '赵六', 21, 92.0);
```
查询所有数据：
```sql
SELECT * FROM students;
```
多表：
```sql
CREATE TABLE scores (
id INT PRIMARY KEY,
student_id INT,
subject VARCHAR(50),
score FLOAT,
FOREIGN KEY (student_id) REFERENCES students(id)
);
```
插入数据：
```sql
INSERT INTO scores (id, student_id, subject, score) VALUES
(1, 1, '语文', 85.0),
(2, 1, '数学', 90.5),
(3, 2, '语文', 80.0),
(4, 2, '数学', 88.0),
(5, 3, '语文', 78.5),
(6, 3, '数学', 92.0),
(7, 4, '语文', 90.5),
(8, 4, '数学', 85.0),
(9, 5, '语文', 82.0),
(10, 5, '数学', 89.5);
```
查询所有数据：
```sql
SELECT * FROM scores;
```
分类汇总排序查：
```sql
SELECT subject, COUNT(*) AS count, AVG(score) AS average_score FROM scores GROUP BY subject ORDER BY average_score DESC;
```
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