(1)查询users表，列出用户的所有信息。
SELECT * FROM users;
(2)查询goods表，列出商品编号、名称和进货量（库存量+销售量，列名为purchases).
SELECT gid, gname, (gquantity + gsale_qty) AS purchases FROM goods;
(3）查询users表，找出2000年以后出生的用户，列出用户名、性别和所在城市。
SELECT uname, ugender, ucity
FROM users
WHERE ubirthday >= '2000-01-01';
(4）查询users表，找出使用QQ邮箱的用户，列出登录名、用户名和邮箱地址。
SELECT ulogin,uname, uemail
FROM users
WHERE uemail LIKE '%@qq.com';
(5）查询users表，找出来自北京、广州和深圳三个城市的用户，列出用户名、性别和所在城市。
SELECT uname, ugender, ucity
FROM users
WHERE ucity IN ('北京', '广州', '深圳');
(6)查询单笔订单金额在5000元以上的订单号。
SELECT oid
FROM orders
WHERE oamount >= 5000;
(7)查询users表，列出积分排名前5的用户名和积分。
SELECT uname, ucredit
FROM users
ORDER BY ucredit DESC
LIMIT 5;
(8）查询users表，按性别统计用户的平均年龄，列出姓名和平均年龄(avg age)。
SELECT ugender, AVG(DATEDIFF(CURDATE(),ubirthday)/365) AS `avg age`
FROM users
GROUP BY ugender;
(9）查询users表，统计各城市的用户人数(num)，并按人数从高到低排序。
SELECT ucity, COUNT(*) AS num
FROM users
GROUP BY ucity
ORDER BY num DESC;
(10)查询users表，列出积分排名前5的用户名、积分和名次(ranking).
SELECT uname, ucredit, ranking
FROM (
SELECT uname, ucredit, RANK() OVER (ORDER BY ucredit DESC) AS ranking
FROM users
) AS ranked_users
WHERE ranking <= 5;
(11)查询goods表，列出所有乐器类商品的id、名称、类别id和类别名称。
SELECT gid, gname, category.cid AS category_id, category.cname AS category_name
FROM goods
INNER JOIN category ON goods.cid = category.cid
WHERE category.cname = '乐器';
(12)查询图书类商品的总销售量(sale_count)。
SELECT SUM(gsale_qty) AS sale_count
FROM goods
INNER JOIN category ON goods.cid = category.cid
WHERE category.cname = '图书';
(13)查询用户“郭辉”的购物车信息，列出商品id、名称、价格和数量。
SELECT cart.gid, goods.gname, goods.gprice, cart.cnum
FROM cart
INNER JOIN goods ON cart.gid = goods.gid
INNER JOIN users ON cart.uid = users.uid
WHERE users.uname = '郭辉';
(14)查询用户“郭辉”的订单信息，列出订单id、订单编号、订单金额和下单日期。
SELECT orders.oid, orders.ocode, orders.oamount, orders.ordertime
FROM orders
INNER JOIN users ON orders.uid = users.uid
WHERE users.uname = '郭辉';
(15）查询订单号为“O210912082615101”的订单详情，列出商品名称、价格和购买量。
SELECT goods.gname, goods.gprice, ordersitem.inum
FROM ordersitem
INNER JOIN goods ON ordersitem.gid = goods.gid
INNER JOIN orders ON ordersitem.oid = orders.oid
WHERE orders.ocode = 'O210912082615101';
(16)查询购买过“平凡的世界”商品的用户信息，列出用户名、性别和出生日期
SELECT users.uname, users.ugender, users.ubirthday
FROM users
INNER JOIN orders ON users.uid = orders.uid
INNER JOIN ordersitem ON orders.oid = ordersitem.oid
INNER JOIN goods ON ordersitem.gid = goods.gid
WHERE goods.gname = '平凡的世界';
(17)使用联合查询，查询来自北京、广州和深圳3个城市的用户，列出用户名、性别和所在城市。
SELECT uname, ugender, ucity
FROM users
WHERE ucity = '北京'
UNION
SELECT uname, ugender, ucity
FROM users
WHERE ucity = '广州'
UNION
SELECT uname, ugender, ucity
FROM users
WHERE ucity = '深圳';
来源地址：https://blog.csdn.net/weixin_57444167/article/details/130419767
