省份城市试题
#省份表
-> select * from province;
+----+----------+
| id | province |
+----+----------+
| 1 | 广东 |
| 2 | 湖南 |
| 3 | 湖北 |
+----+----------+
3 rows in set
mysql> #城市表
-> select * from city;
+----+------+------------+
| id | city | provinceid |
+----+------+------------+
| 1 | 广州 | 1 |
| 2 | 深圳 | 1 |
| 3 | 惠州 | 1 |
| 4 | 长沙 | 2 |
| 5 | 武汉 | 3 |
+----+------+------------+
#获得所有的城市并得出该城市的省
-> select c.id,c.city,p.province from city c left join province p on c.provinceid=p.id;
+----+------+----------+
| id | city | province |
+----+------+----------+
| 1 | 广州 | 广东 |
| 2 | 深圳 | 广东 |
| 3 | 惠州 | 广东 |
| 4 | 长沙 | 湖南 |
| 5 | 武汉 | 湖北 |
+----+------+----------+
#获得所有省份，并查处该省份所有城市的个数
-> select p.id,p.province,count(*) from city c left join province p on c.provinceid=p.id group by c.provinceid;
+----+----------+----------+
| id | province | count(*) |
+----+----------+----------+
| 1 | 广东 | 3 |
| 2 | 湖南 | 1 |
| 3 | 湖北 | 1 |
+----+----------+----------+
学生分数表
mysql> select * from score;
+----+----------+-------+-------+
| id | username | class | score |
+----+----------+-------+-------+
| 1 | 张三 | 语文 | 81 |
| 2 | 张三 | 数学 | 75 |
| 3 | 李四 | 语文 | 76 |
| 4 | 李四 | 数学 | 90 |
| 5 | 王五 | 语文 | 81 |
| 6 | 王五 | 数学 | 100 |
| 7 | 王五 | 英语 | 90 |
+----+----------+-------+-------+
获得学生的总分数,平均分数
-> select id,username,sum(score),avg(score) from score group by username;
+----+----------+------------+------------+
| id | username | sum(score) | avg(score) |
+----+----------+------------+------------+
| 1 | 张三 | 156 | 78.0000 |
| 3 | 李四 | 166 | 83.0000 |
| 5 | 王五 | 271 | 90.3333 |
+----+----------+------------+------------+
#获得所有分数都大于80的学生的名字
select * from score group by username having min(score)>80;
+----+----------+-------+-------+
| id | username | class | score |
+----+----------+-------+-------+
| 5 | 王五 | 语文 | 81 |
+----+----------+-------+-------+
select distinct(username) from score where username not in (select username from score where score<80);
+----------+
| username |
+----------+
| 王五 |
+----------+
包含值
select * from test;
+----+---------+
| id | data |
+----+---------+
| 1 | 2 |
| 2 | 1,2 |
| 3 | 1,22,23 |
| 4 | 2,34 |
| 5 | 1,2,6 |
+----+---------+
5 rows in set
获得2的所有数据，但不要22等
mysql> select * from test where FIND_IN_SET(2,data);
+----+-------+
| id | data |
+----+-------+
| 1 | 2 |
| 2 | 1,2 |
| 4 | 2,34 |
| 5 | 1,2,6 |
+----+-------+