数据库查询

-- 查询单价小于20的数据条数 SELECT COUNT(*) FROM book WHERE price < 20 -- 查询平均单价 SELECT AVG(price) FROM book -- 查询最大单价 SELECT MAX(price) FROM book -- 查询最小单价 SELECT MIN(price) FROM book -- 库存数量总和 SELECT SUM(quantity) FROM book