MySQL 增删改查（单表）

1、sql 新增语句

• 表中插入数据
  • insert into + 表名 values(字段1value1，字段2value1，字段3value1)，(字段1value2，字段2value2，字段3value2)

mysql> insert into t_student values(1,"zhangsan",18,"boy"),(2,"wangwu",20,"girl");

mysql> select * from t_student;

+----+----------+------+------+
| id | name     | age  | sex  |
+----+----------+------+------+
|  1 | zhangsan |   18 | boy  |
|  2 | wangwu   |   20 | girl |
+----+----------+------+------+

• 对表中指定字段插入数据
  • insert into +表名(字段1，字段2) values (字段1值，字段2值)

mysql> insert into t_student(id,name,age,sex)values(3,"zhaoliu",19,"boy");

mysql> select * from t_student;

+----+----------+------+------+
| id | name     | age  | sex  |
+----+----------+------+------+
|  1 | zhangsan |   18 | boy  |
|  2 | wangwu   |   20 | girl |
|  3 | zhaoliu  |   19 | boy  |
+----+----------+------+------+

2、sql 删除语句

• 删除表中指定数据
  • delete from + 表名 where 条件　　
  • delete from + 表名　　--->     清空表

# 删除 t_student 表中 id = 4 的数据
mysql> delete from t_student where id = 4

# 清空 t_student 表
mysql> delete from t_student

3、sql 修改语句

• 更新表中指定字段数据
  • update + 表名 set 字段名=值 where 条件　　

# 修改 t_student 表中 wangwu 的性别为 boy
mysql> update t_student set sex = "boy" where name = "wangwu";

mysql> select * from t_student;

+----+----------+------+------+
| id | name     | age  | sex  |
+----+----------+------+------+
|  1 | zhangsan |   18 | boy  |
|  2 | wangwu   |   20 | boy  |
|  3 | zhaoliu  |   19 | boy  |
+----+----------+------+------+

4、sql 单表查询语句

• 查询表中所有数据
  • select * from + 表名
    • * 代表所有

# 查询 t_student 表中所有数据
mysql> select * from t_student;

+----+----------+------+------+
| id | name     | age  | sex  |
+----+----------+------+------+
|  1 | zhangsan |   18 | boy  |
|  2 | wangwu   |   20 | boy  |
|  3 | zhaoliu  |   19 | boy  |
+----+----------+------+------+

•  查询某个字段的数据
  • select 字段 from + 表名

# 查询出 t_student 表中 name 字段的所有数据
mysql> select name from t_student;

+----------+
| name     |
+----------+
| zhangsan |
| wangwu   |
| zhaoliu  |
+----------+

• 查询多个字段的数据
  • select 字段1，字段2 from + 表名

# 查询出 t_student 表中 name，age 两个字段的所有数据
mysql> select name,age from t_student;

+----------+------+
| name     | age  |
+----------+------+
| zhangsan |   18 |
| wangwu   |   20 |
| zhaoliu  |   19 |
+----------+------+

• 查询满足某个条件的所有数据
  • select * from + 表名 where 字段=值
    
    • where 后面接满足的条件

mysql> select age,sex from t_student where name = "zhaoliu";

+------+------+
| age  | sex  |
+------+------+
|   19 | boy  |
+------+------+

• 查询不满足某个条件的所有数据
  • select * from + 表名 where 字段 != value
    • != 代表不等于，也可以用符号 <> 代表不等于　　

mysql> select age,sex from t_student where name != "zhaoliu";
+------+------+
| age  | sex  |
+------+------+
|   18 | boy  |
|   20 | boy  |
+------+------+

mysql> select age,sex from t_student where name <> "zhaoliu";
+------+------+
| age  | sex  |
+------+------+
|   18 | boy  |
|   20 | boy  |
+------+------+

• 查询同时满足多个条件数据
  • select * from + 表名 where 条件1 and 条件2
    • and 关键字左右的两个条件必须同时满足

# 查询出性别为 boy 且班级为 2 班的学生信息
mysql> select * from t_student where sex = "boy" and class = 2;

+----+---------+------+------+-------+
| id | name    | age  | sex  | class |
+----+---------+------+------+-------+
|  3 | zhaoliu |   19 | boy  | 2     |
+----+---------+------+------+-------+

• 查询满足至少 1 个条件的数据
  • select * from + 表名 where 条件1 or 条件2
    • or 关键字左右的两个条件至少满足 1 个，否则返回空

# 查询出年纪为 18 岁 或者班级为 2 班的学生信息
mysql> select * from t_student where age = 18 or class = 2;

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
+----+----------+------+------+-------+

• 查询一个条件范围内的数据
  • select * from + 表名 where 字段 between m and n
    
    • between...and ... 指定一个范围

# 查询出年纪在 19 - 20 之间的学生信息
mysql> select * from t_student where age between 19 and 20;

+----+---------+------+------+-------+
| id | name    | age  | sex  | class |
+----+---------+------+------+-------+
|  2 | wangwu  |   20 | boy  | 1     |
|  3 | zhaoliu |   19 | boy  | 2     |
+----+---------+------+------+-------+

• 查询字段满足在指定的集合中的数据
  • select * from + 表名 where 字段 in（值1，值2，值3）

mysql> select * from t_student where age in (18,19);

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
+----+----------+------+------+-------+

• 查询字段不满足在指定集合中的数据
  • select * from + 表名 where 字段 not in （值1，值2，值3）

mysql> select * from t_student where age not in (18,19);

+----+--------+------+------+-------+
| id | name   | age  | sex  | class |
+----+--------+------+------+-------+
|  2 | wangwu |   20 | boy  | 1     |
+----+--------+------+------+-------+

• 查询字段值为空的数据
  • select * from + 表名 where 字段 is null　　
    • 注意：字段是空不能写成 字段 = null

mysql> select * from t_student where class is NULL;

+----+------+------+------+-------+
| id | name | age  | sex  | class |
+----+------+------+------+-------+
|  4 | lisi |   22 | girl | NULL  |
+----+------+------+------+-------+

• 查询字段不为空的数据
  • select * from + 表名 where 字段 is not null

mysql> select * from t_student where class is not NULL;

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
|  2 | wangwu   |   20 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
+----+----------+------+------+-------+

• 查询某个字段模糊匹配成功的数据　　
  • select * from +表名 where 字段 like "%值%"
    • % 用于匹配字段开头和结尾

# 查询出表中姓 zhang 的学生信息
mysql> select * from t_student where name like "zhang%";

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
+----+----------+------+------+-------+

# 查询出表中姓名中带有 ng 的学生信息
mysql> select * from t_student where name like "%ng%";

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
|  2 | wangwu   |   20 | boy  | 1     |
+----+----------+------+------+-------+

• 查询限定的数量的数据
  • select * from + 表名 limit m，n　　　　
    • m 指下标，n 指限定的数量，下标为 m 的开始的 n 条数据

# 查询出表中 第 2，3 两行学生信息
mysql> select * from t_student limit 1,2;

+----+---------+------+------+-------+
| id | name    | age  | sex  | class |
+----+---------+------+------+-------+
|  2 | wangwu  |   20 | boy  | 1     |
|  3 | zhaoliu |   19 | boy  | 2     |
+----+---------+------+------+-------+

• 查询的数据根据某个字段从小到大排序
  • select * from + 表名 order by 字段 asc　　
    • order by ...asc 从小到大排序

# 查询表数据，按照 age 字段升序排序
mysql> select * from t_student order by age asc;

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  1 | zhangsan |   18 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
|  2 | wangwu   |   20 | boy  | 1     |
|  4 | lisi     |   22 | girl | NULL  |
+----+----------+------+------+-------+

• 查询的数据根据某个字段从大到小排序
  • select * from + 表名 order by 字段 desc　　
    • order by ... desc 从大到小排序

# 查询表数据，按照 age 字段降序排序
mysql> select * from t_student order by age desc;

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  4 | lisi     |   22 | girl | NULL  |
|  2 | wangwu   |   20 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
|  1 | zhangsan |   18 | boy  | 1     |
+----+----------+------+------+-------+

• 查询的数据根据某个字段进行分组
  • select * from + 表名 group by 字段
    • group by ... 根据条件分组

mysql> select * from t_student group by class;

+----+----------+------+------+-------+
| id | name     | age  | sex  | class |
+----+----------+------+------+-------+
|  4 | lisi     |   22 | girl | NULL  |
|  1 | zhangsan |   18 | boy  | 1     |
|  3 | zhaoliu  |   19 | boy  | 2     |
+----+----------+------+------+-------+

• 查询的数据根据某个字段进行分组再条件过滤
  • select * from + 表名 group by 字段 having 条件
    • having 跟在 group by 后面，作用相当于 where

mysql> select * from t_student group by class having sex = "girl";

+----+------+------+------+-------+
| id | name | age  | sex  | class |
+----+------+------+------+-------+
|  4 | lisi |   22 | girl | NULL  |
+----+------+------+------+-------+

• 聚合函数
  • 统计查询数据的数量　　
    • select count(*) from + 表名

# 统计表中有多少行数据
mysql> select count(*) from t_student;

+----------+
| count(*) |
+----------+
|        4 |
+----------+

• • 查询某个字段求和
    
    • select sum(字段) from + 表名

# 求出所有学员年纪之和
mysql> select sum(age) from t_student;

+----------+
| sum(age) |
+----------+
|       79 |
+----------+

• • 查询某个字段进行平均值
    
    • select avg(字段) from + 表名

# 求出平均年纪
mysql> select avg(age) from t_student;

+----------+
| avg(age) |
+----------+
|  19.7500 |
+----------+

• • 查询某个字段最大值
    
    • select max(字段) from + 表名

# 求出最大年纪
mysql> select max(age) from t_student;

+----------+
| max(age) |
+----------+
|       22 |
+----------+

• • 查询某个字段最小值
    
    • select min(字段) from + 表名

# 求出最小年纪
mysql> select min(age) from t_student;

+----------+
| min(age) |
+----------+
|       18 |
+----------+

• • 对某个字段进行去重
    
    • select distinct(字段) from + 表名

# 对 class 字段去重
mysql> select distinct(class) from t_student;

+-------+
| class |
+-------+
| 1     |
| 2     |
| NULL  |
+-------+