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MYSQL 表

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1、创建表

1.1、创建表基本语法

CREATE TABLE tablename (column_name_1 column_type_1 constraints,
column_name_2 column_type_2 constraints , ……)


column_name 是列的名字
column_type 是列的数据类型
contraints 是这个列的约束条件

1.1.1、创建一张简单的表

mysql> create table orders (ordername varchar(10),createtime date,ordermoney decimal(10,2),ordernumber int(2));
Query OK, 0 rows affected (0.23 sec)

1.1.2、查看创建表定义

结构化定义:

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| Field       | Type          | Null | Key | Default | Extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(10)   | YES  |     | NULL    |       |
| createtime  | date          | YES  |     | NULL    |       |
| ordermoney  | decimal(10,2) | YES  |     | NULL    |       |
| ordernumber | int(2)        | YES  |     | NULL    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

表详细定义:

查看详细的表定义:

mysql> show create table orders \G;
*************************** 1. row ***************************
       Table: orders
Create Table: CREATE TABLE `orders` (
  `ordername` varchar(10) DEFAULT NULL,
  `createtime` date DEFAULT NULL,
  `ordermoney` decimal(10,2) DEFAULT NULL,
  `ordernumber` int(2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

ERROR:
No query specified


由此可以看到表的  ENGINE(存储引擎)是InnoDB

         CHARSET(字符集)是Latin1

\G”选项的含义是使得记录能够按照字段竖着排列,对于内容比较长的记录更易于显示。

2、删除表

命令:

DROP TABLE tablename


删除orders:

mysql> drop table orders
    -> ;
Query OK, 0 rows affected (0.14 sec)


3、修改表

3.1、修改表类型命令

ALTER TABLE tablename MODIFY [COLUMN] column_definition [FIRST | AFTER col_name]


例:修改表 orders name 字段定义,将 varchar(10)改为 varchar(20)

mysql> alter table orders modify ordername varchar(20);
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| Field       | Type          | Null | Key | Default | Extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | YES  |     | NULL    |       |
| createtime  | date          | YES  |     | NULL    |       |
| ordermoney  | decimal(10,2) | YES  |     | NULL    |       |
| ordernumber | int(2)        | YES  |     | NULL    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

3.2、字段改名命令

ALTER TABLE tablename CHANGE [COLUMN] old_col_name column_definition
[FIRST|AFTER col_name]


例:orders 上将ordernumber修改为ordernumbers

mysql> alter table orders change column ordernumber ordernumbers int(4);
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc orders;
+--------------+---------------+------+-----+---------+-------+
| Field        | Type          | Null | Key | Default | Extra |
+--------------+---------------+------+-----+---------+-------+
| ordername    | varchar(20)   | YES  |     | NULL    |       |
| createtime   | date          | YES  |     | NULL    |       |
| ordermoney   | decimal(10,2) | YES  |     | NULL    |       |
| ordernumbers | int(4)        | YES  |     | NULL    |       |
+--------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)


特别说明:change 和 modify 都可以修改表的定义,不同的是 change 后面需要写两次列名,不方便。但是 change 的优点是可以修改列名称,modify 则不能。

3.3、增加表字段命令

ALTER TABLE tablename ADD [COLUMN] column_definition [FIRST | AFTER col_name]


例:orders 上新增加字段 username,类型为 varchar(3)

mysql> alter table orders add column username varchar(30);
Query OK, 0 rows affected (0.39 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| Field       | Type          | Null | Key | Default | Extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | YES  |     | NULL    |       |
| createtime  | date          | YES  |     | NULL    |       |
| ordermoney  | decimal(10,2) | YES  |     | NULL    |       |
| ordernumber | int(2)        | YES  |     | NULL    |       |
| username    | varchar(30)   | YES  |     | NULL    |       |
+-------------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

3.4、删除表列字段命令

ALTER TABLE tablename DROP [COLUMN] col_name


例:orders 上删除字段 username

mysql> alter table orders drop column username;
Query OK, 0 rows affected (0.53 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| Field       | Type          | Null | Key | Default | Extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | YES  |     | NULL    |       |
| createtime  | date          | YES  |     | NULL    |       |
| ordermoney  | decimal(10,2) | YES  |     | NULL    |       |
| ordernumber | int(2)        | YES  |     | NULL    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

3.5、表改名命令

ALTER TABLE tablename RENAME [TO] new_tablename


例:orders 名字改为goodsorders

mysql> alter table orders rename goodsorders;
Query OK, 0 rows affected (0.16 sec)

mysql> desc orders;
ERROR 1146 (42S02): Table 'ordermanage.orders' doesn't exist
mysql> desc goodsorders;
+--------------+---------------+------+-----+---------+-------+
| Field        | Type          | Null | Key | Default | Extra |
+--------------+---------------+------+-----+---------+-------+
| ordername    | varchar(20)   | YES  |     | NULL    |       |
| createtime   | date          | YES  |     | NULL    |       |
| ordermoney   | decimal(10,2) | YES  |     | NULL    |       |
| ordernumbers | int(4)        | YES  |     | NULL    |       |
+--------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
 


4、DML 语句

插入(insert)、查询(select)、更新(update)、删除(delete

4.1、插入记录 命令

INSERT INTO tablename (field1,field2,……fieldn) VALUES(value1,value2,……valuesn);


例:goodsorders 中插入一条记录,ordername zhangcreatetime2021-05-12ordermoney100.00,ordernumbers为:1

mysql> insert into goodsorders (ordername,createtime,ordermoney,ordernumbers) values('zhang','2021-05-12',100.00,1);
Query OK, 1 row affected (0.03 sec)


也可以省略(field1,field2,……fieldn)这一部分

mysql> insert into goodsorders  values('zhang1','2021-05-12',1001.00,11);
Query OK, 1 row affected (0.05 sec)

4.2、查看插入数据命令

4.2.1、查询全部

SELECT * FROM tablename [WHERE CONDITION]


例:查看goodsorders中所有插入数据

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |     100.00 |            1 |
| zhang1    | 2021-05-12 |    1001.00 |           11 |
+-----------+------------+------------+--------------+
2 rows in set (0.00 sec)


其中“*”表示要将所有的记录都选出来

4.2.2、查询不重复记录命令关键字

distinct


例:查询非goodsorders中非重复创建时间(createtime)的数据

mysql> select  * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2020-05-12 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.00 sec)

mysql> select distinct createtime from goodsorders;
+------------+
| createtime |
+------------+
| 2021-03-11 |
| 2020-05-12 |
| 2020-03-12 |
| 2020-03-11 |
+------------+
4 rows in set (0.00 sec)

由此可以看到,将重复的一条时间数据2021-03-11去掉了

4.2.3、多条件查询关键字

where 后面的条件是一个字段的‘='比较,还可以使用>、<、>=、<=、!=等比较运算符;
多个条件之间还可以使用 or、and 等逻辑运算符进行多条件联合查询,

例:查询非goodsorders ordername='li'并且createtime2020-03-11

mysql> select * from goodsorders where ordername='li'and createtime ='2020-03-11';
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
1 row in set (0.00 sec)

4.2.4、排序查询命名

SELECT * FROM tablename [WHERE CONDITION] [ORDER BY field1 [DESC|ASC] , field2 
[DESC|ASC],……fieldn [DESC|ASC]]


例:goodsorders表中的记录按照创建时间高低进行排序显示

mysql> select * from goodsorders order by createtime;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-05-12 |      70.00 |           15 |
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.01 sec)

4.2.5、显示一部分,而不是全部,指令

SELECT ……[LIMIT offset_start,row_count]


offset_start 表示记录的起始偏移量
row_count 表示显示的行数

例如1:显示 goodsorders表中按照 createtiem 排序后的前 3 条记录:

mysql> select * from goodsorders order by createtime limit 3;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-05-12 |      70.00 |           15 |
+-----------+------------+------------+--------------+
3 rows in set (0.00 sec)


例如2:如果要显示 goodsorders表中按照 createtiem 排序后 从第二条记录开始,显示3条数据:

mysql> select * from goodsorders order by createtime limit 2,3;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-05-12 |      70.00 |           15 |
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
3 rows in set (0.00 sec)

4.2.6、统计数据,聚合指令

SELECT [field1,field2,……fieldn] fun_name 
FROM tablename
[WHERE where_contition]
[GROUP BY field1,field2,……fieldn
[WITH ROLLUP]]
[HAVING where_contition]


参数说明:

注意:having 和 where 的区别在于 having 是对聚合后的结果进行条件的过滤,而 where 是在聚合前就对记录进行过滤,如果逻辑允许,我们尽可能用 where 先过滤记录,这样因为结果集减小,将对聚合的效率大大提高,最后再根据逻辑看是否用 having 进行再过滤。

例1:查询统计goodsorders表中,记录总数

mysql> select count(1) from goodsorders;
+----------+
| count(1) |
+----------+
|        5 |
+----------+
1 row in set (0.00 sec)


例2:在此基础上,按照创建日期(createtime)进行分组统计

mysql> select createtime,count(1) from goodsorders group by createtime;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2020-03-11 |        1 |
| 2020-03-12 |        1 |
| 2020-05-12 |        1 |
| 2021-03-11 |        2 |
+------------+----------+
4 rows in set (0.00 sec)


例3:在此基础上,既要按照创建日期(cretetime)进行分组统计,又要计算总数

mysql> select createtime,count(1) from goodsorders group by createtime with rollup;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2020-03-11 |        1 |
| 2020-03-12 |        1 |
| 2020-05-12 |        1 |
| 2021-03-11 |        2 |
| NULL       |        5 |
+------------+----------+
5 rows in set (0.02 sec)


最有一行,null所展示的数字,就是总数

例4:按照创建日期(createtime)进行分组统计,并且数量大于1

mysql> select createtime,count(1) from goodsorders group by createtime having count(1)>1;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2021-03-11 |        2 |
+------------+----------+
1 row in set (0.00 sec)


例5:查询goodsorders表中,订单金额(ordermoney)的总额、最低额、最高额

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2020-05-12 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.00 sec)

mysql> select sum(ordermoney),max(ordermoney),min(ordermoney) from goodsorders;
+-----------------+-----------------+-----------------+
| sum(ordermoney) | max(ordermoney) | min(ordermoney) |
+-----------------+-----------------+-----------------+
|          330.00 |           70.00 |           50.00 |
+-----------------+-----------------+-----------------+
1 row in set (0.02 sec)

4.2.7、表连接

 例1:现在我们又创建一张用户表(member),使用goodorders进行左连接,查询关联的用户表信息

mysql> select * from member;
+------+------------+
| id   | membername |
+------+------------+
| 15   | zhang      |
| 1    | li         |
| 13   | liss       |
+------+------------+
3 rows in set (0.00 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2020-03-11 |      70.00 |           15 | 3        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
5 rows in set (0.00 sec)

mysql> select * from goodsorders left join member on goodsorders.memberid = member.id;
+-----------+------------+------------+--------------+----------+------+------------+
| ordername | createtime | ordermoney | ordernumbers | memberid | id   | membername |
+-----------+------------+------------+--------------+----------+------+------------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       | 15   | zhang      |
| li        | 2020-05-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2021-03-11 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-11 |      70.00 |           15 | 3        | NULL | NULL       |
+-----------+------------+------------+--------------+----------+------+------------+
5 rows in set (0.00 sec)

 例2membergoodsorders中数据不变,我们再来看一下右连接的查询,以及结果:

mysql> select * from goodsorders right join member on goodsorders.memberid = member.id;
+-----------+------------+------------+--------------+----------+------+------------+
| ordername | createtime | ordermoney | ordernumbers | memberid | id   | membername |
+-----------+------------+------------+--------------+----------+------+------------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       | 15   | zhang      |
| li        | 2020-05-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2021-03-11 |      70.00 |           15 | 1        | 1    | li         |
| NULL      | NULL       |       NULL |         NULL | NULL     | 13   | liss       |
+-----------+------------+------------+--------------+----------+------+------------+
5 rows in set (0.00 sec)

这里发生了翻转,变为左侧goodsorders 表中的一条数据为空了

4.2.8、子查询,相关关键字

主要包括 innot in=!=existsnot exists

例:goodsorders表中查询所有用户在memeber表中的记录

mysql> select * from member;
+------+------------+
| id   | membername |
+------+------------+
| 15   | zhang      |
| 1    | li         |
| 13   | liss       |
+------+------------+
3 rows in set (0.00 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2020-03-11 |      70.00 |           15 | 3        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
5 rows in set (0.00 sec)

mysql> select * from goodsorders where memberid in(select id from member);
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
4 rows in set (0.05 sec)

4.2.9、记录联合,指令

SELECT * FROM t1
UNION|UNION ALL
SELECT * FROM t2
……
UNION|UNION ALL
SELECT * FROM tn;


UNION UNION ALL 的主要区别:

     UNION ALL 是把结果集直接合并在一起,
     UNION 是将UNION ALL 后的结果进行一次 DISTINCT,去除重复记录后的结果。

例1:member表和goodsorders表中的用户编号id(memberid)的集合显示出来

mysql> select memberid from goodsorders union all select id from member;
+----------+
| memberid |
+----------+
| 15       |
| 1        |
| 1        |
| 3        |
| 1        |
| 15       |
| 1        |
| 13       |
+----------+
8 rows in set (0.00 sec)

例2:如果希望将上面的结果去掉重复记录后显示

mysql> select memberid from goodsorders union select id from member;
+----------+
| memberid |
+----------+
| 15       |
| 1        |
| 3        |
| 13       |
+----------+
4 rows in set (0.00 sec)

4.3、更新记录命令

UPDATE tablename SET field1=value1,field2.=value2,……fieldn=valuen [WHERE CONDITION]


例:将表 goodsorders ordernamezhang的订单金额(ordermoney)改为50

mysql> update goodsorders set ordermoney=50.00 where ordername='zhang';
Query OK, 1 row affected (0.09 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |      50.00 |            1 |
| zhang1    | 2021-05-12 |    1001.00 |           11 |
+-----------+------------+------------+--------------+
2 rows in set (0.00 sec)

更新时,如遇到错误代码1175:

Error Code: 1175. You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column. To disable safe mode, toggle the option in Preferences

解决方法:

1、先进行状体查询:

show variables like 'SQL_SAFE_UPDATES';


2、执行下面的sql,关闭safe-updates模式:

SET SQL_SAFE_UPDATES = 0;


或者

SET SQL_SAFE_UPDATES = false;
 

4.4、删除记录命名

DELETE FROM tablename [WHERE CONDITION]


例:将表 goodsorders ordernamezhang1的记录全部删除

mysql> delete from goodsorders where ordername = 'zhang1';
Query OK, 1 row affected (0.06 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |      50.00 |            1 |
+-----------+------------+------------+--------------+
1 row in set (0.02 sec)
 


4.5、初始化表

例:将表中的所有数据清空

mysql> select * from varc;
+------+------+
| v    | c    |
+------+------+
| abc  | abc  |
+------+------+
1 row in set (0.03 sec)

mysql> truncate table varc;
Query OK, 0 rows affected (0.25 sec)

mysql> select * from varc;
Empty set (0.00 sec)
 

5、DCL 语句

DCL语句主要是为了管理数据库系统中的操作对象权限

5.1创建数据库用户

例:创建一个数据库用户 user1,初始密码为123,具有对 ordermanage 数据库中所有表的 SELECT/INSERT 权限:

mysql> grant select,insert on ordermanage.* to 'user1'@'localhost' identified by '123';
Query OK, 0 rows affected, 1 warning (0.06 sec)

mysql> exit
Bye


C:\Program Files\MySQL\MySQL Server 5.7\bin>mysql -uuser1 -p123
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 82
Server version: 5.7.17-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| ordermanage        |
+--------------------+
2 rows in set (0.00 sec)

在此基础上,将此用户(user1)的insert权限进行收回

mysql> revoke insert on ordermanage.* from 'user1'@'localhost';
Query OK, 0 rows affected (0.02 sec)

mysql> exit
Bye

C:\Program Files\MySQL\MySQL Server 5.7\bin>mysql -uuser1 -p123
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 84
Server version: 5.7.17-log MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use ordermanage;
Database changed

mysql> insert into member values('11','ss');
ERROR 1142 (42000): INSERT command denied to user 'user1'@'localhost' for table 'member'
mysql>

由此可以看出插入权限不足,插入失败

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