Linux学习-MySQL之SQL语句
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查询语句类型
- 简单查询
- 多表查询
- 子查询
简单查询
select * from tb_name;
select field1,field2… from tb_name; 投影
select * from tb_name where qualification; 选择
FROM子句
要查询的关系 表(简单查询)，多个表(多表查询)，其它SELECT语句(子查询)
WHERE子句
布尔关系表达式[=|>|>=|<|<=|<>]
逻辑表达式[and(&&) | or(||) | not ]
between… and …
like ‘char%’ 以char开头
%：表示任意长度任意字符
_：表示任意一个字符
regexp | rlike 正则表达式
IN
IS NULL | IS NOT NULL
ORDER BY FIELD_NAME ｛ASC | DESC}
字段别名：AS
LIMIT子句： LIMIT[offset,]count —offset（偏移量）
聚合：AVG（平均）MAX（最大）MIN（最小）SUM（和）COUNT（统计个数）
GROUP BY：分组用来做聚合计算
HAVING QUALITATION 对分组结果再进行过滤
SELECT语句执行次序
#基础表信息
#老师表
mysql> desc tutors;
+--------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------+------+-----+---------+----------------+
| TID | tinyint(4) | NO | PRI | NULL | auto_increment |
| Tname | varchar(30) | YES | | NULL | |
| Gender | enum('M','F') | YES | | NULL | |
| Age | tinyint(4) | YES | | NULL | |
+--------+---------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
#学生表
mysql> desc student;
+------------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------------+------+-----+---------+----------------+
| sid | tinyint(4) | NO | PRI | NULL | auto_increment |
| Name | varchar(30) | YES | | NULL | |
| Age | tinyint(4) | YES | | NULL | |
| Gender | enum('M','F') | YES | | NULL | |
| CID1 | tinyint(4) | YES | | NULL | |
| CID2 | tinyint(4) | YES | | NULL | |
| TID | tinyint(4) | YES | | NULL | |
| CreateTime | datetime | YES | | NULL | |
+------------+---------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)
#课程表
mysql> desc courses;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| CID | tinyint(4) | NO | PRI | NULL | auto_increment |
| Cname | varchar(30) | YES | | NULL | |
| TID | tinyint(4) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
#学生表数据
mysql> select * from student;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
10 rows in set (0.00 sec)
#老师表数据
mysql> select * from tutors;
+-----+--------------+--------+------+
| TID | Tname | Gender | Age |
+-----+--------------+--------+------+
| 1 | HongQigong | M | 93 |
| 2 | HuangYaoshi | M | 63 |
| 3 | Miejueshitai | F | 72 |
| 4 | OuYangfeng | M | 76 |
| 5 | YiDeng | M | 90 |
| 6 | YuCanghai | M | 56 |
| 7 | Jinlunfawang | M | 67 |
| 8 | HuYidao | M | 42 |
| 9 | NingZhongze | M | 49 |
+-----+--------------+--------+------+
9 rows in set (0.00 sec)
#课程表数据
mysql> select * from courses;
+-----+------------------+------+
| CID | Cname | TID |
+-----+------------------+------+
| 1 | Hamagong | 2 |
| 2 | Taijiquan | 3 |
| 3 | Yiyangzhi | 6 |
| 4 | Jinshejianfa | 1 |
| 5 | Qianzhuwandushou | 4 |
| 6 | Qishangquan | 5 |
| 7 | Qiankundanuoyi | 7 |
| 8 | Wanliduxing | 8 |
| 9 | Pixiejianfa | 3 |
| 10 | Jiuyinbaiguzhua | 7 |
+-----+------------------+------+
10 rows in set (0.00 sec)
#查询年龄大于19的用户
mysql> select * from student where age>19;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
5 rows in set (0.00 sec)
#查询年龄小于18并且Gender为'F'
mysql> select * from student where age<18 and Gender='F';
+-----+-----------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-----------+------+--------+------+------+------+---------------------+
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
+-----+-----------+------+--------+------+------+------+---------------------+
1 row in set (0.00 sec)
#查询年龄在18至25之间的用户
mysql> select * from student where age between 18 and 25;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
6 rows in set (0.00 sec)
#查询Name以Y开头的用户
mysql> select * from student where Name like 'Y%';
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
3 rows in set (0.00 sec)
#查询以Y开头，且Y后面有4个字符
mysql> select * from student where Name like 'Y____';
+-----+-------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------+------+--------+------+------+------+---------------------+
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------+------+--------+------+------+------+---------------------+
1 row in set (0.00 sec)
#基于正则表达式查找以Y开头的名字信息
mysql> select Name from student where Name regexp '^Y';
+-------------+
| Name |
+-------------+
| YangGuo |
| YueLingshan |
| YiLin |
+-------------+
3 rows in set (0.00 sec)
#通过IN关键字查找集合内的数据
mysql> select * from student where Age in (25,19,18);
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
4 rows in set (0.00 sec)
#通过IS NULL判断是否为空值
mysql> select * from student where CID2 is null;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
2 rows in set (0.00 sec)
#IS NOT NULL判断非空
mysql> select * from student where CID2 is not null;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
8 rows in set (0.00 sec)
#order by 实现排序，默认为升序排序
mysql> select * from student order by Age;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
10 rows in set (0.00 sec)
#根据年龄降序排序
mysql> select * from student order by Age desc;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
10 rows in set (0.00 sec)
#通过AS给字段起别名
mysql> select Name as student_name from student;
+--------------+
| student_name |
+--------------+
| GuoJing |
| YangGuo |
| DingDian |
| HuFei |
| GuangRong |
| YueLingshan |
| ZhangWuji |
| Xuzhu |
| LingHuchong |
| YiLin |
+--------------+
10 rows in set (0.00 sec)
mysql> select 2+1 as SUM;
+-----+
| SUM |
+-----+
| 3 |
+-----+
1 row in set (0.00 sec)
#LIMIT显示前两行数据
mysql> select * from student limit 2;
+-----+---------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+---------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
+-----+---------+------+--------+------+------+------+---------------------+
2 rows in set (0.00 sec)
#LIMIT[offset,]count,偏移offset个，显示count个
mysql> select * from student limit 2,3;
+-----+-----------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-----------+------+--------+------+------+------+---------------------+
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
+-----+-----------+------+--------+------+------+------+---------------------+
3 rows in set (0.00 sec)
#聚合函数使用
mysql> select avg(Age) from student;
+----------+
| avg(Age) |
+----------+
| 21.3000 |
+----------+
1 row in set (0.00 sec)
mysql> select count(Age) from student;
+------------+
| count(Age) |
+------------+
| 10 |
+------------+
1 row in set (0.00 sec)
mysql> select max(Age) from student;
+----------+
| max(Age) |
+----------+
| 31 |
+----------+
1 row in set (0.00 sec)
mysql> select min(Age) from student;
+----------+
| min(Age) |
+----------+
| 16 |
+----------+
1 row in set (0.00 sec)
mysql> select sum(Age) from student;
+----------+
| sum(Age) |
+----------+
| 213 |
+----------+
1 row in set (0.00 sec)
#分组计算平均年龄
mysql> select avg(Age) from student group by Gender;
+----------+
| avg(Age) |
+----------+
| 22.8571 |
| 17.6667 |
+----------+
2 rows in set (0.00 sec)
#判断课程的选课人数
mysql> select count(CID1) as 人数,CID1 from student group by CID1;
+--------+------+
| 人数 | CID1 |
+--------+------+
| 1 | 1 |
| 3 | 2 |
| 1 | 5 |
| 1 | 6 |
| 2 | 8 |
| 1 | 11 |
| 1 | 18 |
+--------+------+
7 rows in set (0.00 sec)
#Having结合Group By 使用，对Group by的结果进行再次过滤
mysql> select count(CID1) as persons,CID1 from student group by CID1 having persons>1;
+---------+------+
| persons | CID1 |
+---------+------+
| 3 | 2 |
| 2 | 8 |
+---------+------+
2 rows in set (0.00 sec)
多表查询
连接：
交叉连接：笛卡尔乘积
自然连接：将两张表
外连接：
左外连接【…left join … on …】
右外连接【…right join… on …】
自连接
#基础表信息
#CID1表示学生选择的第1门课，CID2表示学生选择的第2门课
mysql> select * from student;
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 1 | GuoJing | 19 | M | 2 | 7 | 3 | 2021-06-21 00:00:00 |
| 2 | YangGuo | 17 | M | 2 | 3 | 1 | 2021-06-21 00:00:00 |
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 5 | GuangRong | 16 | F | 5 | 9 | 9 | 2021-06-21 00:00:00 |
| 6 | YueLingshan | 18 | F | 8 | 4 | NULL | 2021-06-21 00:00:00 |
| 7 | ZhangWuji | 20 | M | 1 | 7 | NULL | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
| 10 | YiLin | 19 | F | 18 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
10 rows in set (0.00 sec)
mysql> select * from courses;
+-----+------------------+------+
| CID | Cname | TID |
+-----+------------------+------+
| 1 | Hamagong | 2 |
| 2 | Taijiquan | 3 |
| 3 | Yiyangzhi | 6 |
| 4 | Jinshejianfa | 1 |
| 5 | Qianzhuwandushou | 4 |
| 6 | Qishangquan | 5 |
| 7 | Qiankundanuoyi | 7 |
| 8 | Wanliduxing | 8 |
| 9 | Pixiejianfa | 3 |
| 10 | Jiuyinbaiguzhua | 7 |
+-----+------------------+------+
10 rows in set (0.00 sec)
#查询学生表中的学生学习的第一门课程即课程名称
mysql> select student.Name,courses.Cname from student,courses where student.CID1=coursess.CID;
+-------------+------------------+
| Name | Cname |
+-------------+------------------+
| GuoJing | Taijiquan |
| YangGuo | Taijiquan |
| DingDian | Qishangquan |
| HuFei | Wanliduxing |
| GuangRong | Qianzhuwandushou |
| YueLingshan | Wanliduxing |
| ZhangWuji | Hamagong |
| Xuzhu | Taijiquan |
+-------------+------------------+
8 rows in set (0.00 sec)
mysql> select s.Name,c.Cname from student as s,courses as c where s.CID1=c.CID;
+-------------+------------------+
| Name | Cname |
+-------------+------------------+
| GuoJing | Taijiquan |
| YangGuo | Taijiquan |
| DingDian | Qishangquan |
| HuFei | Wanliduxing |
| GuangRong | Qianzhuwandushou |
| YueLingshan | Wanliduxing |
| ZhangWuji | Hamagong |
| Xuzhu | Taijiquan |
+-------------+------------------+
8 rows in set (0.00 sec)
#left...join...on,通过on来指定条件
mysql> select s.Name,c.Cname from student as s left join courses as c on s.CID1=c.CID;
+-------------+------------------+
| Name | Cname |
+-------------+------------------+
| GuoJing | Taijiquan |
| YangGuo | Taijiquan |
| DingDian | Qishangquan |
| HuFei | Wanliduxing |
| GuangRong | Qianzhuwandushou |
| YueLingshan | Wanliduxing |
| ZhangWuji | Hamagong |
| Xuzhu | Taijiquan |
| LingHuchong | NULL |
| YiLin | NULL |
+-------------+------------------+
10 rows in set (0.00 sec)
mysql> select s.Name,c.Cname from student as s right join courses as c on s.CID1=c.CID;
+-------------+------------------+
| Name | Cname |
+-------------+------------------+
| GuoJing | Taijiquan |
| YangGuo | Taijiquan |
| DingDian | Qishangquan |
| HuFei | Wanliduxing |
| GuangRong | Qianzhuwandushou |
| YueLingshan | Wanliduxing |
| ZhangWuji | Hamagong |
| Xuzhu | Taijiquan |
| NULL | Yiyangzhi |
| NULL | Jinshejianfa |
| NULL | Qiankundanuoyi |
| NULL | Pixiejianfa |
| NULL | Jiuyinbaiguzhua |
+-------------+------------------+
13 rows in set (0.00 sec)
#自连接
mysql> select s.Name as Student,c.Name as Teacher from student as s,student as c where s.TID=c.sid;
+-----------+-------------+
| Student | Teacher |
+-----------+-------------+
| GuoJing | DingDian |
| YangGuo | GuoJing |
| DingDian | ZhangWuji |
| HuFei | GuangRong |
| GuangRong | LingHuchong |
+-----------+-------------+
5 rows in set (0.00 sec)
子查询
比较操作中使用子查询，子查询只能返回单个值
IN中使用子查询
FROM使用子查询
#查询年龄中大于所有同学平均年龄的同学
mysql> select * from student where Age > (select avg(age) from student);
+-----+-------------+------+--------+------+------+------+---------------------+
| sid | Name | Age | Gender | CID1 | CID2 | TID | CreateTime |
+-----+-------------+------+--------+------+------+------+---------------------+
| 3 | DingDian | 25 | M | 6 | 1 | 7 | 2021-06-21 00:00:00 |
| 4 | HuFei | 31 | M | 8 | 10 | 5 | 2021-06-21 00:00:00 |
| 8 | Xuzhu | 26 | M | 2 | 4 | NULL | 2021-06-21 00:00:00 |
| 9 | LingHuchong | 22 | M | 11 | NULL | NULL | 2021-06-21 00:00:00 |
+-----+-------------+------+--------+------+------+------+---------------------+
4 rows in set (0.00 sec)
#From子查询
mysql> select Name,Age from (select Name,Age from student) as t where t.age >20 ;
+-------------+------+
| Name | Age |
+-------------+------+
| DingDian | 25 |
| HuFei | 31 |
| Xuzhu | 26 |
| LingHuchong | 22 |
+-------------+------+
4 rows in set (0.00 sec)
#挑选出courses表中没有被students中的CID2学习的课程的课程名称
mysql> select Cname from courses where CID not in(select distinct CID2 from student where CID2 is not null);
+------------------+
| Cname |
+------------------+
| Taijiquan |
| Qianzhuwandushou |
| Qishangquan |
| Wanliduxing |
+------------------+
4 rows in set (0.00 sec)
#挑选出没有教授任何课程的老师
mysql> select Tname from tutors where TID not in (select distinct TID from courses);
+-------------+
| Tname |
+-------------+
| NingZhongze |
+-------------+
1 row in set (0.00 sec)
#找出students表中CID1有两个或两个以上同学学习了的同一门课程的课程名称
mysql> select Cname from courses as c, (select count(CID1) as CIDsum,CID1 from student group by CID1 having CIDsum>1) as t where t.CID1=c.CID;
+-------------+
| Cname |
+-------------+
| Taijiquan |
| Wanliduxing |
+-------------+
2 rows in set (0.00 sec)
#查询课程表中，学生选择的第一门课中没有选择的课程名称
mysql> select c.Cname,c.CID from courses as c where c.CID not in (select CID1 from studeent);
+-----------------+-----+
| Cname | CID |
+-----------------+-----+
| Yiyangzhi | 3 |
| Jinshejianfa | 4 |
| Qiankundanuoyi | 7 |
| Pixiejianfa | 9 |
| Jiuyinbaiguzhua | 10 |
+-----------------+-----+
5 rows in set (0.00 sec)
#显示每一位老师及其所教授的课程：没有教授的课程保持为NULL
mysql> select t.Tname,c.Cname from tutors as t left join courses as c on c.TID=t.TID;
+--------------+------------------+
| Tname | Cname |
+--------------+------------------+
| HuangYaoshi | Hamagong |
| Miejueshitai | Taijiquan |
| YuCanghai | Yiyangzhi |
| HongQigong | Jinshejianfa |
| OuYangfeng | Qianzhuwandushou |
| YiDeng | Qishangquan |
| Jinlunfawang | Qiankundanuoyi |
| HuYidao | Wanliduxing |
| Miejueshitai | Pixiejianfa |
| Jinlunfawang | Jiuyinbaiguzhua |
| NingZhongze | NULL |
+--------------+------------------+
11 rows in set (0.00 sec)
#显示每一个课程及其相关的老师，没有老师教授的课程将其老师显示为空
mysql> select c.Cname,t.Tname from courses as c left join tutors as t on c.TID=t.TID;
+------------------+--------------+
| Cname | Tname |
+------------------+--------------+
| Hamagong | HuangYaoshi |
| Taijiquan | Miejueshitai |
| Yiyangzhi | YuCanghai |
| Jinshejianfa | HongQigong |
| Qianzhuwandushou | OuYangfeng |
| Qishangquan | YiDeng |
| Qiankundanuoyi | Jinlunfawang |
| Wanliduxing | HuYidao |
| Pixiejianfa | Miejueshitai |
| Jiuyinbaiguzhua | Jinlunfawang |
+------------------+--------------+
#显示每位同学CID1课程的课程名及其讲授了相关课程的老师的名称
mysql> select m.Cname as CourseName,t.Tname as TeacherName from (select s.CID1,c.Cname,c.TID from student as s,courses as c where s.CID1=c.CID) as m,tutors as t where t.TID=m.TID group by CourseName;
+------------------+--------------+
| CourseName | TeacherName |
+------------------+--------------+
| Hamagong | HuangYaoshi |
| Qianzhuwandushou | OuYangfeng |
| Qishangquan | YiDeng |
| Taijiquan | Miejueshitai |
| Wanliduxing | HuYidao |
+------------------+--------------+
5 rows in set (0.00 sec)
#查看创建表语句
mysql> show create table student;
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`sid` tinyint(4) NOT NULL AUTO_INCREMENT,
`Name` varchar(30) DEFAULT NULL,
`Age` tinyint(4) DEFAULT NULL,
`Gender` enum('M','F') DEFAULT NULL,
`CID1` tinyint(4) DEFAULT NULL,
`CID2` tinyint(4) DEFAULT NULL,
`TID` tinyint(4) DEFAULT NULL,
`CreateTime` datetime DEFAULT NULL,
PRIMARY KEY (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=gbk |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
联合查询
UNION
视图— 存储下来的SELECT语句
基于基表的查询结果
VIEW
MySQL客户端命令
# -e 客户端执行mysql语句
[root@mail ~]# mysql -uroot -p -e 'create database edb';
Enter password:
[root@mail ~]# mysql -uroot -p -e 'show databases';
Enter password:
+--------------------+
| Database |
+--------------------+
| information_schema |
| edb |
| extmail |
| filemanager |
| mydb |
| mysql |
| performance_schema |
| students |
| test |
| vsftpd |
+--------------------+
#通过shell脚本动态向student表中插入数据
#!/bin/bash
while true
do
random_str=$(($RANDOM%100))
student_name="student$random_str"
random_CID1=$(($RANDOM%10))
random_CID2=$(($RANDOM%10))
random_TID=$(($RANDOM%10))
gender_str='F'
if [ $random_str%2 == 0 ]; then
gender_str='M'
fi
sql_info="insert into students.student(Name,Age,Gender,CID1,CID2,TID) values ('$student_name',$random_str,'$gender_str',$random_CID1,$random_CID2,$random_TID);"
mysql -uroot -p123456 -e "$sql_info" 2>/dev/null
sleep 2
done
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