MySQL---表的增查改删（CRUD基础）-Toy模板网

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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
MySQL---表的增查改删（CRUD基础）,MySQL,1024程序员节,mysql

新增（Create）

insert into 表名 values（值，值，值...）;

注：这里值的类型和个数要和表的列的类型和个数匹配。

单行数据 + 全列插入

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

注：

在SQL中没有字符串类型，所以既可以用‘ ’来引用字符串，又可以使用“ ”来引用字符串；

还可以直接插入中文字符（需要把数据库字符集改为UTF-8）

进行插入操作时，插入值的个数和类型要于表中字段的个数和类型匹配

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)

注：比一条一条插入更快

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)

注：

通配符* 表示匹配所有的列，即查询所有列，把所有的数据都查询出来；

这是一个危险操作（当数据量大的时候）：进行此操作的时候，服务器要先读取磁盘，把这些数据都查出来，再通过网卡，把这些数据传输给客户端，由于数据量非常大，极有可能把磁盘IO（输入输出）吃满，或者网络带宽吃满。这时其他数据就无法正常返回了，最直观的感受就是客户端感受到卡顿。

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)

注：当我们查询时省去一些不必要的列时，就可以节约大量的磁盘IO和网络带宽了。

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)

注：as可以写着，也可以省略。建议写着！

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)

注：当用distinct指定多个列时，必须是这几个列的值同时相同时才会去重。

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)

注：

升序排序末尾加asc 但默认是升序排序可以省略，降序排序末尾加desc

在SQL中，拿NULL和其他类型进行混合计算，结果仍然是NULL

在select操作中，如果没有使用order by 那么查询结果的顺序是不确定的。

条件查询

select* from 表名 where 条件;

引入where子句，对条件进行筛选，即：用where子句对最初的每一行查询结果进行筛选，如果满足条件，就把这一行放入到最终的查询结果；如果不满足条件，则舍弃这一行；最后返回最终查询结果。

比较运算符

MySQL---表的增查改删（CRUD基础）,MySQL,1024程序员节,mysql

注：

在SQL中没有== 使用=进行比较

在SQL中，NULL = NULL 结果还是NUULL ，相当于false； NULL <=> NULL 结果是true

like进行模糊匹配，匹配过程中可以带上通配符

逻辑运算符

MySQL---表的增查改删（CRUD基础）,MySQL,1024程序员节,mysql

注：

在where条件中，可以使用表达式，但不能使用别名；

and的优先级高于or，在使用时注意次序或者加（）

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)

注： % 可以替代任意个字符，_ 可以替代任意一个字符

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)

注：

直接使用 = 来进行匹配是不能正确进行筛选的

使用 <=> 可以正确和NULL匹配

使用 is NULL也可以正确和NULL匹配

分页查询

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

N：返回结果的条数 M：跳过M条结果再开始返回

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)

注：select* 这样的操作容易把数据库搞挂了，除了select*外，其他的查询操作只要你返回的结果足够多，都有可能把数据库搞挂；即使你加上了where子句进行筛选，但是返回的结果仍然可能很多。最保险的办法就是加上limit

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)

注： update后面的where条件很重要。加上条件，表示修改符合条件某些行；不加条件，表示修改所有行。

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)

注：文章来源地址https://www.toymoban.com/news/detail-720644.html

delete后面的 where 条件很重要。加上条件，表示删除符合条件某些行；不加条件，表示删除表中的全部信息。

delete from 表名；表示删除表内的所有信息，但是表还在。
drop table 表名；表示删除整个表，表也不存在了。

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