数据库小问题，可以看一下

按单位统计出该单位的读者人数。
查找读者数在两人及以上的部门名称和读者人数。
分别统计各出版社的图书的平均单价和总金额。
对借阅表现按读者编号，再按条码统计图书的借阅次数，并显示小计。
将图书表按数量从大到小排序。
将借阅表按节约状态排序，状态相同，再按借阅日期从小到大排序。

稍等,这些语句都是刚开始接触sql的时候基础语法，等到你学到TSQL高级部分，可以不用这种做法实现
有兴趣的话看看这个帖子：https://learn.microsoft.com/zh-cn/sql/t-sql/tutorial-writing-transact-sql-statements?view=sql-server-ver16

1.SELECT unit, COUNT(DISTINCT reader_id) AS reader_count
FROM readers
GROUP BY unit
2；SELECT department, COUNT(DISTINCT reader_id) AS reader_count
FROM readers
GROUP BY department
HAVING COUNT(DISTINCT reader_id) >= 2
3;SELECT publisher, AVG(price) AS avg_price, SUM(price) AS total_price
FROM books
GROUP BY publisher
4;SELECT reader_id, book_id, COUNT(*) AS borrow_count
FROM borrows
GROUP BY reader_id, book_id WITH ROLLUP
5;SELECT * FROM books ORDER BY quantity DESC
6;SELECT * FROM borrows ORDER BY saved DESC, borrow_date ASC