MySQL学习总结之路（第二章：表）
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目录
MySQL学习总结之路（第三章：数据类型）
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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>createtable 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
1.1.2.1、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 inset (0.00 sec)
1.1.2.2、表详细定义
查看详细的表定义
mysql> show createtable orders \G; ***************************1. row ***************************Table: orders CreateTable: CREATETABLE `orders` ( `ordername` varchar(10) DEFAULTNULL, `createtime` date DEFAULTNULL, `ordermoney` decimal(10,2) DEFAULTNULL, `ordernumber` int(2) DEFAULTNULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1 1 row inset (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>droptable 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 的 name 字段定义，将 varchar(10)改为 varchar(20)：
mysql>altertable 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 inset (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：表 orders 上将ordernumber修改为ordernumbers
mysql>altertable 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 inset (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：表 orders 上新增加字段 username，类型为 varchar(3)：
mysql>altertable orders addcolumn 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 inset (0.00 sec)
3.4、删除表列字段命令
ALTER
TABLE tablename DROP[COLUMN]col_name
例：表 orders 上删除字段 username：
mysql>altertable orders dropcolumn 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 inset (0.00 sec)
3.5、表改名命令
ALTER
TABLE tablename RENAME [TO] new_tablename
例：表 orders 名字改为goodsorders
mysql>altertable 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：表 goodsorders 中插入一条记录，ordername 为zhang，createtime为2021-05-12，ordermoney为100.00,ordernumbers为：1
mysql>insertinto 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>insertinto goodsorders values(‘zhang1‘,‘2021-05-12‘,1001.00,11); Query OK, 1 row affected (0.05 sec)
4.2、查看插入数据命名
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 inset (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 inset (0.00 sec) mysql>selectdistinct createtime from goodsorders; +------------+| createtime |+------------+|2021-03-11||2020-05-12||2020-03-12||2020-03-11|+------------+4 rows inset (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中 ordername=‘li‘并且createtime为2020-03-11
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 inset (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：把 goodsorders表中的记录按照创建时间高低进行排序显示
mysql>select*from goodsorders orderby 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 inset (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 orderby 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 inset (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 orderby 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 inset (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>selectcount(1) from goodsorders; +----------+|count(1) |+----------+|5|+----------+1 row inset (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 groupby createtime; +------------+----------+| createtime |count(1) |+------------+----------+|2020-03-11|1||2020-03-12|1||2020-05-12|1||2021-03-11|2|+------------+----------+4 rows inset (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 groupby 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 inset (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 groupby createtime havingcount(1)>1; +------------+----------+| createtime |count(1) |+------------+----------+|2021-03-11|2|+------------+----------+1 row inset (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 inset (0.00 sec) mysql>selectsum(ordermoney),max(ordermoney),min(ordermoney) from goodsorders; +-----------------+-----------------+-----------------+|sum(ordermoney) |max(ordermoney) |min(ordermoney) |+-----------------+-----------------+-----------------+|330.00|70.00|50.00|+-----------------+-----------------+-----------------+1 row inset (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 inset (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 inset (0.00 sec) mysql>select*from goodsorders leftjoin 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 inset (0.00 sec)
例2：member和goodsorders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 rightjoin 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 inset (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 in、notin、=、!=、exists、notexists 等
例：从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 inset (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 inset (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 inset (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 和 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：将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 unionallselect id from member; +----------+| memberid |+----------+|15||1||1||3||1||15||1||13|+----------+8 rows inset (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 unionselect id from member; +----------+| memberid |+----------+|15||1||3||13|+----------+4 rows inset (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 中ordername为zhang的订单金额（ordermoney）改为50
mysql>update goodsorders set ordermoney=50.00where 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 inset (0.00 sec)
4.4、删除记录命名
DELETE
FROM tablename [WHERE CONDITION]
例：将表 goodsorders 中ordername为zhang1的记录全部删除
mysql>deletefrom 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 inset (0.02 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>grantselect,inserton 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 endwith ; or \g. Your MySQL connection id is82 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 inset (0.00 sec)
在此基础上，将此用户（user1）的insert权限进行收回
mysql>revokeinserton 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 endwith ; or \g. Your MySQL connection id is84 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>insertinto member values(‘11‘,‘ss‘); ERROR 1142 (42000): INSERT command denied touser‘user1‘@‘localhost‘fortable‘member‘ mysql>
由此可以看出插入权限不足，插入失败
此章节完事儿嘞
原文：https://www.cnblogs.com/19930521zhang/p/14756371.html
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