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文章目录

• 什么是CRUD？
• 新增（Create）
• • 单行数据 + 全列插入
  • 多行数据 + 指定列插入
• 查询（Retrieve）
• • 全列查询
  • 指定列查询
  • 查询字段为表达式
  • 起别名查询
  • 去重查询
  • 排序查询
  • 条件查询
  • 分页查询
• 修改（Update）
• 删除（Delete）

什么是CRUD？

CRUD，即增加（Create）、查找（Retrieve）、修改（Update）、删除（Delete）四个单词的首字母缩写。

在进行下面所有操作的前提都是得选中一个数据库，并且已经创建了可以用来操作的表。
默认我们现在已经创建了learning数据库，在数据库中有一张student表。后续操作都基于此进行

新增（Create）

insert into 表名 values（值，值，值...）;

单行数据 + 全列插入

mysql> insert into student values (1,"zhangsan");
Query OK, 1 row affected (0.00 sec)

多行数据 + 指定列插入

mysql> insert into student values (1,"zhangsan")，（2，"lisi"）,(3,"wangwu");
Query OK, 3 row affected (0.00 sec)

查询（Retrieve）

MySQL是一个客户端—服务器结构的程序，显示在客户端的查询结果是一个“临时表”，服务器端的数据并不是这样的组织形式。

全列查询

select* from 表名;

mysql> select * from student;
+------+----------+
| id   | name     |
+------+----------+
|    1 | zhangsan |
|    2 | lisi     |
|    3 | wangwu   |
+------+----------+
3 rows in set (0.00 sec)

指定列查询

select 列名，列名，列名.... from 表名;

mysql> select id from student;
+------+
| id   |
+------+
|    1 |
|    2 |
|    3 |
+------+
3 rows in set (0.00 sec)

查询字段为表达式

select 表达式 from 表名;

• 演示此操作需要创建一个新的表：

mysql> create table exam_result (id int, name varchar(20), chinese decimal(3,1),math decimal(3,1), english decimal(3,1));
Query OK, 0 rows affected (0.01 sec)
//decimal（3，1） 表示共有三位有效数字，保留一位小数。 比如：32.1、10.5

• 查看一下表结构：

mysql> desc exam_result;
+---------+--------------+------+-----+---------+-------+
| Field   | Type         | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| id      | int(11)      | YES  |     | NULL    |       |
| name    | varchar(20)  | YES  |     | NULL    |       |
| chinese | decimal(3,1) | YES  |     | NULL    |       |
| math    | decimal(3,1) | YES  |     | NULL    |       |
| english | decimal(3,1) | YES  |     | NULL    |       |
+---------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

• 插入数据

mysql> INSERT INTO exam_result (id,name, chinese, math, english) VALUES
    ->  (1,'zhangsan', 67, 98, 56),
    ->  (2,'lisi', 87.5, 78, 77),
    ->  (3,'wangwu', 88, 98.5, 90),
    ->  (4,'zhaoliu', 82, 84, 67),
    ->  (5,'sunqi', 55.5, 85, 45),
    ->  (6,'zhouba', 70, 73, 78.5),
    ->  (7,'wujiu', 75, 65, 30);
Query OK, 7 rows affected (0.00 sec)
Records: 7  Duplicates: 0  Warnings: 0

• 查询表内全部数据

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
+------+-----------+---------+------+---------+
7 rows in set (0.00 sec)

• 带表达式的查询：让所有人的语文成绩+10分

mysql> select name,chinese + 10 from exam_result;
+-----------+--------------+
| name      | chinese + 10 |
+-----------+--------------+
| zhangsan  |         77.0 |
| lisi      |         97.5 |
| wangwu    |         98.0 |
| zhaoliu   |         92.0 |
| sunqi     |         65.5 |
| zhouba    |         80.0 |
| wujiu     |         85.0 |
+-----------+--------------+
7 rows in set (0.00 sec)

起别名查询

select 表达式 as 别名 from 表名;

• 普通情况查询语、数、英三科总分

mysql> select name, chinese + math + english from exam_result;
+-----------+--------------------------+
| name      | chinese + math + english |
+-----------+--------------------------+
| zhangsan   |                    221.0 |
| lisi       |                    242.5 |
| wangwu     |                    276.5 |
| zhaoliu    |                    233.0 |
| sunqi      |                    185.5 |
| zhouba     |                    221.5 |
| wujiu      |                    170.0 |
+-----------+--------------------------+
7 rows in set (0.00 sec)

• 起别名查询语、数、英三科总分

mysql> select name, chinese + english + math as total from exam_result;
+-----------+-------+
| name      | total |
+-----------+-------+
| zhangsan  | 221.0 |
| lisi      | 242.5 |
| wangwu    | 276.5 |
| zhaoliu   | 233.0 |
| sunqi     | 185.5 |
| zhouba    | 221.5 |
| wujiu     | 170.0 |
+-----------+-------+
7 rows in set (0.00 sec)

去重查询

select distinct 列名 from 表名;

• 演示此操作需增加相同信息

mysql> insert into exam_result (name, math) values ('zhangsan', 98.0);
Query OK, 1 row affected (0.00 sec)

• 查看当前表的全部信息

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

• 进行去重查询

mysql> select distinct name, math from exam_result;
+-----------+------+
| name      | math |
+-----------+------+
| zhangsan  | 98.0 |
| lisi      | 78.0 |
| wangwu    | 98.5 |
| zhaoliu   | 84.0 |
| sunqi     | 85.0 |
| zhouba    | 73.0 |
| wujiu     | 65.0 |
+-----------+------+
7 rows in set (0.00 sec)

排序查询

select 列名 from 表名 order by 列名;

• 按语文成绩升序排序

mysql> select * from exam_result order by chinese;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

• 按语文成绩降序排序

mysql> select * from exam_result order by chinese desc;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

• order by 也可以针对别名进行排序

mysql>  select name, chinese + math + english as total from exam_result order by total desc;
+-----------+-------+
| name      | total |
+-----------+-------+
| wangwu    | 276.5 |
| lisi      | 242.5 |
| zhaoliu   | 233.0 |
| zhouba    | 221.5 |
| zhangsan  | 221.0 |
| sunqi     | 185.5 |
| wujiu     | 170.0 |
| zhangsan  |  NULL |
+-----------+-------+
8 rows in set (0.00 sec)

• order by 进行排序的时候还可以指定多个列进行排序 效果是：先以第一列为标准进行比较，如果第一列不分胜负，那么继续按照第二列进行比较，一次类推

mysql> select * from exam_result order by math desc,chinese;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    3 |  wangwu   |    88.0 | 98.5 |    90.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

条件查询

select* from 表名 where 条件;

• 比较运算符

• 逻辑运算符

• 基本查询：查询语文成绩比英语成绩好的人

mysql> select * from exam_result where chinese > english;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
+------+-----------+---------+------+---------+
5 rows in set (0.00 sec)

• and / or查询

mysql> select * from exam_result where chinese > 80 or english > 70 and math > 70;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
+------+-----------+---------+------+---------+
4 rows in set (0.00 sec)

• 范围查询：查询语文成绩在80-90之间的人

mysql> select * from exam_result where chinese >= 80 and chinese <= 90;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
+------+-----------+---------+------+---------+
3 rows in set (0.00 sec)

mysql>  select * from exam_result where chinese between 80 and 90;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
+------+-----------+---------+------+---------+
3 rows in set (0.00 sec)

• in 查询 查询数学成绩是58 或者59 或者98 或者99的人

mysql> select * from exam_result where math in (58,59,98,99);
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan    |    67.0 | 98.0 |    56.0 |
+------+-----------+---------+------+---------+
1 rows in set (0.00 sec)

mysql>  select * from exam_result where math = 58 or math = 59 or math = 98 or math = 99;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan    |    67.0 | 98.0 |    56.0 |
+------+-----------+---------+------+---------+
1 rows in set (0.00 sec)

• 模糊查询like 不一定完全相同，只要有一部分匹配即可。

mysql>  select * from exam_result where name like 'w%';
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    3 | wangwu    |      88 | 98.5 |      90 |
|    7 | wujiu     |      75 |   65 |      30 |
+------+-----------+---------+------+---------+
2 rows in set (0.00 sec)

• NULL的查询

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

mysql> select * from exam_result where chinese = NULL;
Empty set (0.00 sec)

mysql> select * from exam_result where chinese <=> NULL;
+------+--------+---------+------+---------+
| id   | name   | chinese | math | english |
+------+--------+---------+------+---------+
| NULL |zhangsan|    NULL | 98.0 |    NULL |
+------+--------+---------+------+---------+
1 row in set (0.00 sec)

mysql>  select * from exam_result where chinese is NULL;
+------+--------+---------+------+---------+
| id   | name   | chinese | math | english |
+------+--------+---------+------+---------+
| NULL |zhangsan|    NULL | 98.0 |    NULL |
+------+--------+---------+------+---------+
1 row in set (0.00 sec)

分页查询

select 列名 from 表名 limit N offset M;
select 列名 from 表名 limit M,N;

• 从M条开始查询 最多返回N条结果

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

mysql> select * from exam_result limit 3;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 78.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
+------+-----------+---------+------+---------+
3 rows in set (0.00 sec)

mysql> select * from exam_result limit 3 offset 3;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
+------+-----------+---------+------+---------+
3 rows in set (0.00 sec)

修改（Update）

update 表名 set 列名 = 值..... where 条件;

• 把lisi 的数学成绩修改为80分

mysql> update exam_result set math = 80 where name = 'lisi';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    1 | zhangsan  |    67.0 | 98.0 |    56.0 |
|    2 | lisi      |    87.5 | 80.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    82.0 | 84.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
| NULL | zhangsan  |    NULL | 98.0 |    NULL |
+------+-----------+---------+------+---------+
8 rows in set (0.00 sec)

删除（Delete）

delete from 表名 where 条件;

• 删除zhangsan的信息

mysql> delete from exam_result where name = 'zhangsan';
Query OK, 1 row affected (0.00 sec)

mysql> select * from exam_result;
+------+-----------+---------+------+---------+
| id   | name      | chinese | math | english |
+------+-----------+---------+------+---------+
|    2 | lisi      |    87.5 | 80.0 |    77.0 |
|    3 | wangwu    |    88.0 | 98.5 |    90.0 |
|    4 | zhaoliu   |    70.0 | 60.0 |    67.0 |
|    5 | sunqi     |    55.5 | 85.0 |    45.0 |
|    6 | zhouba    |    70.0 | 73.0 |    78.5 |
|    7 | wujiu     |    75.0 | 65.0 |    30.0 |
+------+-----------+---------+------+---------+
6 rows in set (0.00 sec)