Linux—mysql的sql语言单表操作

表操作

DROP TABLE [IF EXISTS] 'tbl_name';
ALTER TABLE 'tbl_name' ###增加字段

字段：

添加字段： add
ADD col1 data_type [FIRST|AFTER col_name]

删除字段： drop

修改字段：

alter（默认值） , change（字段名） , modify（字段属性）

索引:

添加索引： add index
删除索引： drop index

表选项

修改:

查看表上的索引： SHOW INDEXES FROM [db_name.]tbl_name;
查看帮助： Help ALTER TABLE

例子：原表

MariaDB [db1]> desc students;
+-------+---------------------+------+-----+---------+----------------+
| Field | Type                | Null | Key | Default | Extra          |
+-------+---------------------+------+-----+---------+----------------+
| id    | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50)         | NO   |     | NULL    |                |
| sex   | enum('f','m')       | YES  |     | NULL    |                |
| age   | tinyint(3) unsigned | YES  |     | 20      |                |
+-------+---------------------+------+-----+---------+----------------+

增加字段后的表：

MariaDB [db1]> alter table students add mobile char(11) after name;
MariaDB [db1]> desc students;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(50)         | NO   |     | NULL    |                |
| mobile | char(11)            | YES  |     | NULL    |                |
| sex    | enum('f','m')       | YES  |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | 20      |                |
+--------+---------------------+------+-----+---------+----------------+
MariaDB [db1]> show indexes from students\G		###查看表上的索引信息
MariaDB [db1]> alter table students add index(name);    ###添加索引信息

DML语句数据表的操作

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DML: INSERT, DELETE, UPDATE

insert 增加数据库

delete 删除数据库

update 修改数据库

INSERT：

一次插入一行或多行数据

语法

INSERT [L OW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE] 优先级

[INTO] tbl_name [(col_name,...)] 赋值字段的顺序

{VALUES | VALUE} ({expr | DEFAULT},...),(...),... 值的顺序

[ ON DUPLICATE KEY UPDATE 如果重复更新之

col_name=expr

[, col_name=expr] ... ]

简化写法：

INSERT tbl_name [(col1,...)] VALUES (val1,...), (val21,...)

例子：

MariaDB [db1]> insert into students(name,mobile,sex,class,age)values('mage','10010','m',18,25);
MariaDB [db1]> insert into students (name,mobile,sex,class,age)values('马哥','120','f',18,45);
+----+--------+---------+------+-------+------+
| id | name   | mobile  | sex  | class | age  |
+----+--------+---------+------+-------+------+
|  1 | mage   | 10010   | m    |   127 |   25 |
|  2 | mage   | 10010   | m    |    18 |   25 
 6 | wang   | 1380000 | m    |   127 |   48 |
|  7 | 马哥   | 120     | f    |    18 |   45 |
+----+--------+---------+------+-------+------+

跨数据库表复制数据方法：

MariaDB [db1]> insert into students(name,mobile,sex,age,)select name,mobile,sex,age from hellodb.students;
增加数据的另一中写法：
MariaDB [db1]> insert into students set name='han',sex='m';
MariaDB [db1]>select * from students;

UPDATE:修改语句

UPDATE：修改数据库

UPDATE [LOW_PRIORITY] [IGNORE] table_reference
SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]

注意：一定要有限制条件，否则将修改所有行的指定字段

限制条件：WHERE LIMIT

Mysql 选项： -U|--safe-updates| --i-am-a-dummy

MariaDB [db1]> update students set sex='f' where id=9;

|  9 | han    | NULL    | f    |  NULL |   20 |
+----+--------+---------+------+-------+------+
注意：如果不指定 where 条件  则所有字段内容全部修改

修改多个字段

MariaDB [db1]> update students set name='li',sex='m',class='16' where id=3;

****为了避免用户修改文件是忘记加where条件导致数据全部修改我们可以修改配置文件；***

[root@centos7-5 my.cnf.d]# vim mysql-clients.cnf 		
[mysql]
safe-updates

delete 删除语句

DELETE:
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
[WHERE where_condition]
[ORDER BY ...]				排序prder by
[LIMIT row_count]				删除的指定条数；

可先排序再指定删除的行数

注意：一定要有限制条件，否则将清空表中的所有数据

限制条件：WHERE LIMIT

TRUNCATE TABLE tbl_name; 清空表

rruncate table students;

例子：
MariaDB [db1]> delete from students where id=9;
limit的用法
MariaDB [db1]> delete from students limit 3 ;
order by 的用法		先排序后删除
MariaDB [db1]> delete from students order by age limit 1 ;  
先按照年龄排序，排完序，排完之后在删除。

SELECT查询语句

SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]

字段显示可以使用别名：

col1 AS alias1, col2 AS alias2, ...

例子：
MariaDB [hellodb]> select stuid as 学员编号,name 姓名,age 年龄 from students;
+--------------+---------------+--------+
| 学员编号     | 姓名          | 年龄   |
+--------------+---------------+--------+
|            1 | Shi Zhongyu   |     22 |
|            2 | Shi Potian    |     22 |
|            3 | Xie Yanke     |     53 |
|            4 | Ding Dian     |     32 |
|            5 | Yu Yutong     |     26 |
|            6 | Shi Qing      |     46 |
|            7 | Xi Ren        |     19 |

WHERE子句：指明过滤条件以实现“选择”的功能：

过滤条件：布尔型表达式
算术操作符： +, -, *, /, %
比较操作符： =,<=>（相等或都为空） , <>, !=(非标准SQL), >, >=, <, <=
BETWEEN min_num AND max_num
IN (element1, element2, ...)
IS NULL
IS NOT NULL

例子：

where 用法

MariaDB [hellodb]> select * from students where classid=1;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     2 | Shi Potian   |  22 | M      |       1 |         7 |
|    12 | Wen Qingqing |  19 | F      |       1 |      NULL |
|    16 | Xu Zhu       |  21 | M      |       1 |      NULL |
|    22 | Xiao Qiao    |  20 | F      |       1 |      NULL |
+-------+--------------+-----+--------+---------+-----------+

MariaDB [hellodb]> select * from students where age > 30;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     3 | Xie Yanke    |  53 | M      |       2 |        16 |
|     4 | Ding Dian    |  32 | M      |       4 |         4 |
|     6 | Shi Qing     |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
|    25 | Sun Dasheng  | 100 | M      |    NULL |      NULL |
+-------+--------------+-----+--------+---------+-----------+

> < 大于小于号用法

MariaDB [hellodb]> select * from students where age > 30 and age <50;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     4 | Ding Dian    |  32 | M      |       4 |         4 |
|     6 | Shi Qing     |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
+-------+--------------+-----+--------+---------+-----------+

between

MariaDB [hellodb]> select * from students where age between 30 and 50;
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     4 | Ding Dian    |  32 | M      |       4 |         4 |
|     6 | Shi Qing     |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  33 | M      |       2 |      NULL |
+-------+--------------+-----+--------+---------+-----------+

in

MariaDB [hellodb]> select * from students where classid in (1,2,3);
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu  |  22 | M      |       2 |         3 |
|     2 | Shi Potian   |  22 | M      |       1 |         7 |
|     3 | Xie Yanke    |  53 | M      |       2 |        16 |
|     5 | Yu Yutong    |  26 | M      |       3 |         1 |

is null

MariaDB [hellodb]> select * from students where teacherid is null ;
MariaDB [hellodb]> select * from students where teacherid is not null ;

2、DISTINCT 去除重复列

SELECT DISTINCT gender FROM students;
MariaDB [hellodb]> select distinct classid  from students;		##去重
+---------+
| classid |
+---------+
|       2 |
|       1 |
|    NULL |
+---------+

3、LIKE:

%: 任意长度的任意字符
_：任意单个字符

例子：

MariaDB [hellodb]> select *  from students where name like 's%';
+-------+-------------+-----+--------+---------+-----------+
| StuID | Name        | Age | Gender | ClassID | TeacherID |
+-------+-------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu |  22 | M      |       2 |         3 |
|     2 | Shi Potian  |  22 | M      |       1 |         7 |
|     6 | Shi Qing    |  46 | M      |       5 |      NULL |
|    25 | Sun Dasheng | 100 | M      |    NULL |      NULL |
+-------+-------------+-----+--------+---------+-----------+
MariaDB [hellodb]> select *  from students where name like '%o';
+-------+-----------+-----+--------+---------+-----------+
| StuID | Name      | Age | Gender | ClassID | TeacherID |
+-------+-----------+-----+--------+---------+-----------+
|    22 | Xiao Qiao |  20 | F      |       1 |      NULL |
|    23 | Ma Chao   |  23 | M      |       4 |      NULL |
+-------+-----------+-----+--------+---------+-----------+

4、RLIKE：正则表达式，索引失效，不建议使用

MariaDB [hellodb]> select *  from students where name rlike '^s';

5、REGEXP：匹配字符串可用正则表达式书写模式，同上

6、逻辑操作符：

NOT

AND

XOR

order by 排序

ORDER BY: 根据指定的字段对查询结果进行排序

升序： ASC

降序： DESC

例子：

MariaDB [hellodb]> select * from students order by age;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name          | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL |
 6 | Shi Qing      |  46 | M      |       5 |      NULL |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL |
+-------+---------------+-----+--------+---------+-----------+
MariaDB [hellodb]> select * from students order by age desc;		##倒序排序

LIMIT [[offset,]row_count]：对查询的结果进行输出行数数量限制

MariaDB [hellodb]> select * from students order by name limit 3;
+-------+-----------+-----+--------+---------+-----------+
| StuID | Name      | Age | Gender | ClassID | TeacherID |
+-------+-----------+-----+--------+---------+-----------+
|    20 | Diao Chan |  19 | F      |       7 |      NULL |
|     4 | Ding Dian |  32 | M      |       4 |         4 |
|    15 | Duan Yu   |  19 | M      |       4 |      NULL |
+-------+-----------+-----+--------+---------+-----------+

MariaDB [hellodb]> select * from students order by age asc limit 2,3;	
******	跳过前2个只显示后三个****
+-------+--------------+-----+--------+---------+-----------+
| StuID | Name         | Age | Gender | ClassID | TeacherID |
+-------+--------------+-----+--------+---------+-----------+
|    19 | Xue Baochai  |  18 | F      |       6 |      NULL |
|    12 | Wen Qingqing |  19 | F      |       1 |      NULL |
|    10 | Yue Lingshan |  19 | F      |       3 |      NULL |
+-------+--------------+-----+--------+---------+-----------+

group的用法

GROUP：根据指定的条件把查询结果进行“分组”以用于做“聚合”运算

avg(), max(), min(), count(), sum()

HAVING: 对分组聚合运算后的结果指定过滤条件

count(*) ##检索到行中非空值的数目。

MariaDB [hellodb]> select classid,count(*) from students  group by classid  ; 
+---------+----------+
| classid | count(*) |
+---------+----------+
|    NULL |        2 |
|       1 |        4 |
|       2 |        3 |
|       3 |        4 |
|       4 |        4 |
|       5 |        1 |
|       6 |        4 |
|       7 |        3 |
+---------+----------+

例子：

MariaDB [hellodb]> select count(*) from students;		统计students表中的行数
MariaDB [hellodb]> select max(age) from students;		统计最大年龄
MariaDB [hellodb]> select min(age) from students;		统计最小年龄
MariaDB [hellodb]> select courseid,avg(score) from scores where courseid=2 ;
+----------+------------+
| courseid | avg(score) |
+----------+------------+
|        2 |    75.2500 |
+----------+------------+

求和

MariaDB [hellodb]> select courseid,sum(score) from scores where courseid=2 ;
+----------+------------+
| courseid | sum(score) |
+----------+------------+
|        2 |        301 |
+----------+------------+

MariaDB [hellodb]> select classid,age,avg(age) from students  group by classid  ;
先对班级进行分组，分完组之后在在对年龄进行求平均值    分组可以理解成去重
+---------+-----+----------+
| classid | age | avg(age) |
+---------+-----+----------+
|    NULL |  27 |  63.5000 |
|       1 |  22 |  20.5000 |
|       2 |  22 |  36.0000 |
|       3 |  26 |  20.2500 |
|       4 |  32 |  24.7500 |
|       5 |  46 |  46.0000 |
|       6 |  20 |  20.7500 |
|       7 |  17 |  19.6667 |
+---------+-----+----------+

having的用法；适合在查询表中做了group by 分组后使用

MariaDB [hellodb]> select classid,avg(age) from students  group by classid having classid in (1,2) ;
+---------+----------+
| classid | avg(age) |
+---------+----------+
|       1 |  20.5000 |
|       2 |  36.0000 |
+---------+----------+

查看students表中classid和年龄，并对年龄进行平均计算，并对classid进行分组，分组后对平均年龄进行别名的明名，最后显示平均年龄大于30的班级。

MariaDB [hellodb]> select classid,age,avg(age) as avg from students  group by classid having avg > 30 ;
+---------+-----+---------+
| classid | age | avg     |
+---------+-----+---------+
|    NULL |  27 | 63.5000 |
|       2 |  22 | 36.0000 |
|       5 |  46 | 46.0000 |
+---------+-----+---------+

(5) 显示TeacherID非空的同学的相关信息

(6) 以年龄排序后，显示年龄最大的前10位同学的信息

(7) 查询年龄大于等于20岁，小于等于25岁的同学的信息

第五题：
MariaDB [hellodb]> select stuid,name,teacherid from students where teacherid is not null ;
第六题：
MariaDB [hellodb]> select stuid,name,age from students order by age desc limit 10 ;
+-------+--------------+-----+
| stuid | name         | age |
+-------+--------------+-----+
|    25 | Sun Dasheng  | 100 |
|     3 | Xie Yanke    |  53 |
|     6 | Shi Qing     |  46 |
|    13 | Tian Boguang |  33 |
|     4 | Ding Dian    |  32 |
|    24 | Xu Xian      |  27 |
|     5 | Yu Yutong    |  26 |
|    17 | Lin Chong    |  25 |
|    23 | Ma Chao      |  23 |
|    18 | Hua Rong     |  23 |
+-------+--------------+-----+
第七题；
MariaDB [hellodb]> select stuid,name,age,avg(age) from students where age >= 20 and age <=25 ;
+-------+-------------+------+----------+
| stuid | name        | age  | avg(age) |
+-------+-------------+------+----------+
|     1 | Shi Zhongyu |   22 |  22.1000 |
+-------+-------------+------+----------+

MariaDB [hellodb]> select classid,gender,count(*) from students group by classid,gender;
+---------+--------+----------+
| classid | gender | count(*) |
+---------+--------+----------+
|    NULL | M      |        2 |
|       1 | F      |        2 |
|       1 | M      |        2 |
|       2 | M      |        3 |
|       3 | F      |        3 |
|       3 | M      |        1 |
|       4 | M      |        4 |
|       5 | M      |        1 |
|       6 | F      |        3 |
|       6 | M      |        1 |
|       7 | F      |        2 |
|       7 | M      |        1 |
+---------+--------+----------+

Linux—mysql的sql语言单表操作

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