读者借阅记录,包含读者号(uid)、图书号(bid)、图书标题(title)和借阅日期(date)四个列。 查询每个用户借了多少书 查询借书最多的10位用户 查询每个用户最早几几年借书 查询每个用户每年借书借了几本书 查询平均年借书量最多的十位用户
时间: 2024-10-24 10:12:48 浏览: 13
javaweb图书借阅管理系统课程设计实验报告(20210806184536).pdf
读者借阅记录是一个数据表,用于跟踪用户的借阅信息。它主要包括以下几个方面:
1. **查询每个用户借了多少书**:这可以通过对uid进行分组并计算每个group(用户)的图书数量来完成。SQL语句可能是这样的:
```
SELECT uid, COUNT(*) as borrow_count
FROM reader_borrow_record
GROUP BY uid;
```
2. **查询借书最多的10位用户**:同样通过分组并按borrow_count降序排列,然后取前10名:
```
SELECT uid, borrow_count
FROM (
SELECT uid, COUNT(*) as borrow_count
FROM reader_borrow_record
GROUP BY uid
) as counts
ORDER BY borrow_count DESC
LIMIT 10;
```
3. **查询每个用户最早哪一年借书**:这需要查找每个用户最早的借阅日期(假设日期格式有年份信息):
```
SELECT uid, MIN(date) AS first_book_year
FROM reader_borrow_record
GROUP BY uid;
```
4. **查询每个用户每年借书的数量**:这可能涉及到对日期进行分桶统计,如果数据库支持时间范围聚合函数,例如MySQL的`YEAR()`:
```
SELECT YEAR(date) as year, uid, COUNT(*) as books_per_year
FROM reader_borrow_record
GROUP BY uid, YEAR(date);
```
5. **查询平均年借书量最多的十位用户**:这需要计算每位用户的年度平均借书数,然后按照平均值排序并取前10位:
```
SELECT uid, AVG(books_per_year) as avg_books_per_year
FROM (
SELECT uid, YEAR(date) as year, COUNT(*) as books_per_year
FROM reader_borrow_record
GROUP BY uid, YEAR(date)
) as yearly_counts
GROUP BY uid
ORDER BY avg_books_per_year DESC
LIMIT 10;
```
请注意,实际的SQL语法可能会因使用的数据库系统而略有不同。
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