MySQL 查询语句练习1

Posted 2020-09-30 LCQ

 

1、创建成绩表，字段包括：学生姓名，语文成绩，数学成绩，英语成绩

向表中插入多条数据；
查询：

　　(1) 查询所有学生的数学成绩和总成绩

　　(2) 查询所有学生的语文和数学成绩和，按从高到低排序

　　(3) 查询班级总成绩最高的学生姓名

　　(4) 查询班里所有姓李学生的总成绩最高的姓名

 

创建表

CREATE TABLE grade (
        name VARCHAR(20) NOT NULL ,
        chinese_score FLOAT NOT NULL ,
        math_score FLOAT NOT NULL ,
        english_score FLOAT NOT NULL
        ) CHARACTER SET utf8;    

　　

mysql> DESC grade;
+---------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-------------+------+-----+---------+-------+
| name | varchar(20) | NO | | NULL | |
| chinese_score | float | NO | | NULL | |
| math_score | float | NO | | NULL | |
| english_score | float | NO | | NULL | |
+---------------+-------------+------+-----+---------+-------+

　　

插入记录

INSERT grade VALUES(‘李白‘,88,99,77),(‘杜甫‘,77,88,99),(‘白居易‘,99,88,77);

　　

1、

mysql> SELECT SUM(math_score) FROM grade;
+-----------------+
| SUM(math_score) |
+-----------------+
| 275 |
+-----------------+
1 row in set (0.00 sec)

　　

2、

mysql> SELECT name,chinese_score+math_score AS ‘语文+数学‘ FROM grade ORDER BY chinese_score+grade.math_score DESC ;
+-----------+---------------+
| name | 语文+数学 |
+-----------+---------------+
| 李白 | 187 |
| 白居易 | 187 |
| 杜甫 | 165 |
+-----------+---------------+
3 rows in set (0.00 sec)

　　

3、

mysql> SELECT name AS ‘姓名‘,chinese+math+english AS ‘总分‘ FROM grade WHERE(chinese+math+english=(SELECT MAX(chinese+math+english)FROM grade));
+--------+--------+
| 姓名 | 总分 |
+--------+--------+
| 李白 | 264 |
+--------+--------+
1 row in set (0.00 sec)

 

4、

mysql> SELECT name AS ‘姓名‘,chinese+math+english AS ‘总分‘ FROM grade WHERE(chinese+math+english=(SELECT MAX(chinese+math+english)FROM grade)and name like ‘李%‘);
+--------+--------+
| 姓名 | 总分 |
+--------+--------+
| 李白 | 264 |
+--------+--------+
1 row in set (0.00 sec)

另一种方法，高分排序，取第一个，order by ，limit 1

 

2、创建一张某超市的购物表，字段包括：商品名，购物价格，商品生茶日期，商品分类；

向该表中插入多条数据；

查询：（1）每一类商品花的总价格

（2）统计每类商品各有多少件

（3）统计水果花了多少钱（两种方式实现）

（4）统计购买的2017-01-12日生产的商品中价格最贵的商品（插入的数据中包括2017-01-12生产的商品）

（5）统一购买商品的总价格

 

CREATE TABLE order_menu(
id INT PRIMARY KEY auto_increment,
product_name VARCHAR (20),
price FLOAT(6,2),
born_date DATE,
class VARCHAR (20)
) CHARACTER SET utf8;

INSERT order_menu (product_name,price,born_date,class) VALUES
("苹果",20,20170112,"水果"),
("香蕉",80,20170602,"水果"),
("水壶",120,20170112,"电器"),
("被罩",70,20170612,"床上用品"),
("音响",420,20170112,"电器"),
("床单",55,20170612,"床上用品"),
("草莓",34,20170612,"水果");

mysql> DESC order_menu;
+--------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| product_name | varchar(20) | YES | | NULL | |
| price | float(6,2) | YES | | NULL | |
| born_date | date | YES | | NULL | |
| class | varchar(20) | YES | | NULL | |
+--------------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

　　

1、

mysql> SELECT class,sum(price) FROM order_menu GROUP BY class;
+--------------+------------+
| class | sum(price) |
+--------------+------------+
| 床上用品 | 125.00 |
| 水果 | 134.00 |
| 电器 | 540.00 |
+--------------+------------+
3 rows in set (0.00 sec)

　　

2、

mysql> SELECT class,count(product_name) FROM order_menu GROUP BY class;
+--------------+---------------------+
| class | count(product_name) |
+--------------+---------------------+
| 床上用品 | 2 |
| 水果 | 3 |
| 电器 | 2 |
+--------------+---------------------+
3 rows in set (0.00 sec)

　　

3、

mysql> SELECT sum(price) FROM order_menu WHERE class=‘水果‘;
+------------+
| sum(price) |
+------------+
| 134.00 |
+------------+
1 row in set (0.00 sec)

3、

mysql> SELECT class,sum(price) FROM order_menu GROUP BY class HAVING class=‘水果‘;
+--------+------------+
| class | sum(price) |
+--------+------------+
| 水果 | 134.00 |
+--------+------------+
1 row in set (0.00 sec)

　　

4、

mysql> SELECT product_name,price FROM order_menu WHERE born_date=20170112 ORDER BY price DESC limit 1;
+--------------+--------+
| product_name | price |
+--------------+--------+
| 音响 | 420.00 |
+--------------+--------+
1 row in set (0.00 sec)

　　

5、

mysql> SELECT sum(price) FROM order_menu;
+------------+
| sum(price) |
+------------+
| 799.00 |
+------------+
1 row in set (0.00 sec)