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mysql运算符（作业）
创建表 tmp15 其中包括varchar类型的字段note 和int类型的字段price ，使用运算符对表中不同的字段进行计算；使用逻辑操作符对数据进行逻辑操作；
mysql> create table tmp15(note varchar(20),price int);
query ok, 0 rows affected (0.63 sec)
mysql> select * from tmp15;
+--------+-------+
| note | price |
+--------+-------+
| aa | 20 |
| yus | 30 |
| book | 30 |
| mylife | 30 |
| love | 67 |
| ben | 50 |
+--------+-------+
6 rows in set (0.00 sec)
1.对tmp15表中的整数值字段price进行算术运算
mysql> select avg(price) `平均价格`, sum(price) `价格和`, min(price) `最低价格`,
max(price) `最高价格`from tmp15;
+--------------+-----------+--------------+--------------+
| 平均价格 | 价格和 | 最低价格 | 最高价格 |
+--------------+-----------+--------------+--------------+
| 37.8333 | 227 | 20 | 67 |
+--------------+-----------+--------------+--------------+
1 row in set (0.00 sec)
2.对tmp15中的整型数值字段price进行比较运算
mysql> select 5030;
+----------------+
| 5030 |
+----------------+
| 0 |
+----------------+
1 row in set (0.00 sec)
mysql> select 5030;
+----------------+
| 5030 |
+----------------+
| 1 |
+----------------+
1 row in set (0.00 sec)
mysql> select 5020;
+--------+
| 5020 |
+--------+
| 1 |
+--------+
1 row in set (0.00 sec)
3.判断price值是否落在30~80区间；返回与70和30相比最大的值，判断price是否为in列表（10, 20, 50, 35）中的某个值
1）mysql> select max(price) `最大值` from tmp15 where price between 30 and 70;
+-----------+
| 最大值 |
+-----------+
| 67 |
+-----------+
1 row in set (0.00 sec)
2）mysql> select * from tmp15 where price in(10,20,50,35);
+------+-------+
| note | price |
+------+-------+
| aa | 20 |
| ben | 50 |
+------+-------+
2 rows in set (0.06 sec)
4..对tmp15中的字符串数值字段note进行比较运算，判断表tmp15中note字段是否为空；使用like判断是否以字母'd'开头；使用regexp判断是否以字母'y'尾；判断是否包含字母'g'或者'm'
判断表tmp15中note字段是否为空
mysql> select note from tmp15 where note is not null;
+--------+
| note |
+--------+
| aa |
| yus |
| book |
| mylife |
| love |
| ben |
+--------+
mysql> select note from tmp15 where note is null;
empty set (0.00 sec)
使用like判断是否以字母'a'开头
mysql> select note from tmp15 where note like 'a%';
+------+
| note |
+------+
| aa |
+------+
1 row in set (0.00 sec)
使用regexp判断是否以字母'y'尾
mysql> select 'fo/no' regexp 'y$';
+---------------------+
| 'fo/no' regexp 'y$' |
+---------------------+
| 0 |
+---------------------+
1 row in set (0.06 sec)
判断是否包含字母'g'或者'm'
mysql> select note from tmp15 where note like '%g%' or '%m%';
empty set, 1 warning (0.00 sec)
5.将price字段值与null，0进行逻辑运算
mysql> select *,price && not null from tmp15;
+--------+-------+-------------------+
| note | price | price && not null |
+--------+-------+-------------------+
| aa | 20 | null |
| yus | 30 | null |
| book | 30 | null |
| mylife | 30 | null |
| love | 67 | null |
| ben | 50 | null |
+--------+-------+-------------------+
6 rows in set (0.00 sec)
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