MYSQL 表的全面总结

2022-05-15 0 147
目录
  • 1、创建表
    • 1.1、创建表基本语法
      • 1.1.1、创建一张简单的表
      • 1.1.2、查看创建表定义
  • 2、删除表
    • 3、修改表
      • 3.1、修改表类型命令
        • 3.2、字段改名命令
          • 3.3、增加表字段命令
            • 3.4、删除表列字段命令
              • 3.5、表改名命令
              • 4、DML 语句
                • 4.1、插入记录 命令
                  • 4.2、查看插入数据命令
                    • 4.2.1、查询全部
                    • 4.2.2、查询不重复记录命令关键字
                    • 4.2.3、多条件查询关键字
                    • 4.2.4、排序查询命名
                    • 4.2.5、显示一部分,而不是全部,指令
                    • 4.2.6、统计数据,聚合指令
                    • 4.2.7、表连接
                    • 4.2.8、子查询,相关关键字
                    • 4.2.9、记录联合,指令
                  • 4.3、更新记录命令
                    • 4.4、删除记录命名
                      • 4.5、初始化表
                      • 5、DCL 语句
                        • 5.1创建数据库用户

                        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:

                        • 1、fun_name 表示要做的聚合操作,也就是聚合函数,常用的有 sum(求和)、count(*)(记录数)、max(最大值)、min(最小值)
                        • 2、GROUP BY 关键字表示要进行分类聚合的字段,比如要按照部门分类统计员工数量,部门就应该写在 group by 后面。
                        • 3、WITH ROLLUP 是可选语法,表明是否对分类聚合后的结果进行再汇总。
                        • 4、HAVING 关键字表示对分类后的结果再进行条件的过滤。

                        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

                        • 1、左连接:包含所有的左边表中的记录甚至是右边表中没有和它匹配的记录;关键指令:left join
                        • 2、右连接:包含所有的右边表中的记录甚至是左边表中没有和它匹配的记录;关联指令:right join

                         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';
                        
                        

                        MYSQL 表的全面总结

                        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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