今天整理了一了一下数据表的基本操作，希望能帮助有需要的人！！！！
MySQL 数据库表操作
第1章 表的介绍
MySQL中的表就和我们excel表格中的sheet一样，一个excel里面可以有多个sheet。在MySQL数据库里面，一个库也可以有多个表，每个表中记录了无数条的数据。这些关系型的数据显示为列和行（类似excel表格）。我们队MySQL的表操作就是对一个sheet操作。
第2章 表的操作
2.1查看表
表是存在于数据库中，所以我们看的表应该是在某个库的下面例如：database.sheet表示数据库database下面的sheet表。下面我们来学习SQL命令来查看表：
mysql> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| student |
| test |
| test2 |
+------------------+
3 rows in set (0.01 sec)
mysql> show create tabletest\G
*************************** 1. row***************************
Table:test
Create Table: CREATE TABLE `test` (
`id` int(4)NOT NULL AUTO_INCREMENT,
`name`char(20) NOT NULL,
PRIMARY KEY(`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULTCHARSET=utf8
1 row in set (0.00 sec)
mysql> desc test;
+-------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+----------------+
| id |int(4) | NO | PRI | NULL | auto_increment |
| name |char(20) | NO | | NULL | |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
小结：
1、show tables; #显示库里面包含的所有表
2、desc test; #显示表的结构
3、show create table test; #显示创建表的SQL语句
2.2表的创建
我们可以通过help create or help contents来查看帮助
mysql> create table student_test( id int(4) notnull, name char(20) not null, age tinyint(2) NOT NULL default '0', dept varchar(16) default NULL ); #
创建一个表为student_test，有4个字段
可以通过desc来查看表的结构
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name |char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
2.3表的删除
方法一：drop命令
mysql> drop table student_test;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| student |
| test |
| test2 |
+------------------+
3 rows in set (0.00 sec)
方法二：delete命令
我们用上面表创建的命令重新创建表：student_test
create table student_test( id int(4) not null, namechar(20) not null, age tinyint(2) NOTNULL default '0', dept varchar(16) default NULL );
查看表
show tables
mysql> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| student |
| student_test |
| test |
| test2 |
+------------------+
4 rows in set (0.00 sec)
删除表 delete from 表名： 删除所有记录，表结构还在，写日志，可以恢复的，速度慢
方法三：truncate
truncate talbe 表名 删除表中的所有记录，表结构还在，不写日志，无法找回删除的记录，速度快 小结： delete from 表名： 删除所有记录，表结构还在，写日志，可以恢复的，速度慢 drop talbe 表名： 删除表的结构和数据 truncate talbe 表名 删除表中的所有记录，表结构还在，不写日志，无法找回删除的记录，速度快
使用场合：
当你不再需要该表时， 用 drop;
当你仍要保留该表，但要删除所有记录时， 用 truncate;
当你要删除部分记录时（always with a whereclause), 用 delete.
注意：
对于有主外键关系的表，不能使用truncate而应该使用不带where子句的delete语句，由于truncate不记录在日志中，不能够激活触发器
2.4表的修改
2.4.1添加字段
mysql> alter table student_test add sex char(2)after age; #这里使用了参数after，表示在什么之后插入，如果在第一行
QueryOK, 0 rows affected (0.02 sec) firs参数。
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name |char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| sex | char(2) | YES | | NULL | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
2.4.2修改type类型
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name |char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| sex | char(2) | YES | | NULL | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
mysql> alter tablestudent_test modify sex varchar(4);
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name |char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| sex | varchar(4) | YES | | NULL | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
2.4.3删除部分字段
mysql> alter tablestudent_test drop sex;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name |char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
2.4.4改变表的字符集
mysql> show create table student_test\G
*************************** 1. row***************************
Table:student_test
Create Table: CREATE TABLE `student_test` (
`id` int(4)NOT NULL,
`name`char(20) NOT NULL,
`age`tinyint(2) NOT NULL DEFAULT '0',
`dept`varchar(16) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> alter tablestudent_test CONVERT TO CHARACTER SET latin1;
mysql> show create table student_test\G
*************************** 1. row***************************
Table:student_test
Create Table: CREATE TABLE `student_test` (
`id` int(4)NOT NULL,
`name`char(20) NOT NULL,
`age`tinyint(2) NOT NULL DEFAULT '0',
`dept`varchar(16) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
2.4.5修改字段名字已经type类型
把name字段改成xingming，类型从char改成varchar
mysql> desc student_test;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| name | char(20) | NO | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| dept |varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
mysql> alter table student_test change columnname xingming varchar(40);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student_test;
+----------+-------------+------+-----+---------+-------+
| Field |Type | Null | Key | Default |Extra |
+----------+-------------+------+-----+---------+-------+
| id |int(4) | NO | | NULL | |
| xingming | varchar(40) | YES | | NULL | |
| age |tinyint(2) | NO | | 0 | |
| dept |varchar(16) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
2.4.6表的重命名
把student_test表重命名为stu_test
m
ysql> rename table student_test to stu_test;
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| stu_test |
| student |
| test |
| test2 |
+------------------+
4 rows in set (0.00 sec)
第3章 表数据的操作
3.1insert命令插入数据
数据的表的插入使用命令insert，语法insert into 表名
mysql> insert into stu_testvalues(1,'kirk',28,'male');
Query OK, 1 row affected (0.00 sec)
mysql> select * from stu_test;
+----+----------+-----+------+
| id | xingming | age | dept |
+----+----------+-----+------+
| 1 |kirk | 28 | male |
+----+----------+-----+------+
1 row in set (0.00 sec)
3.1.1插入数据遇到的问题
ERROR 1300 (HY000): Invalid utf8 character string: '\xA1\xAFaaa\xA1\xAF'
解决办法：引号问题’ ’这种是GB2312 , ' '这种是utf-8
ERROR 1366 (HY000): Incorrect stringvalue: '\xC4\xD0' for column 'sex' at row 1
解决办法：show variables like 'chara%';
setcharacter_set_client=gb2312;
该处查看会显示乱码
解决方法：set character_set_results=gb2312;
3.2修改表数据update
mysql> update stu_test setxingming='laowang' where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from stu_test;
+----+----------+-----+------+
| id | xingming | age | dept |
+----+----------+-----+------+
| 1 |laowang | 28 | male |
| 2 |huasheng | 23 | male |
| 3 |dadou | 20 | nv |
+----+----------+-----+------+
3 rows in set (0.00 sec)
第4章 表的查询
4.1条件查询
mysql> select * from stu_test where xingming='dadou';
+----+----------+-----+------+
| id | xingming | age | dept |
+----+----------+-----+------+
| 3 |dadou | 20 | nv |
+----+----------+-----+------+
1 row in set (0.00 sec)
mysql> select xingming,age from stu_test;
+----------+-----+
| xingming | age |
+----------+-----+
| laowang | 28 |
| huasheng | 23 |
| dadou | 20 |
+----------+-----+
3 rows in set (0.00 sec)
+----+----------+-----+------+
| id | xingming | age | dept |
+----+----------+-----+------+
| 1 |laowang | 28 | male |
| 2 |huasheng | 23 | male |
| 3 |dadou | 20 | nv |
| 4 |dadou | 20 | male |
+----+----------+-----+------+
4 rows in set (0.00 sec)
mysql> select 20 from stu_test;
+----+
| 20 |
+----+
| 20 |
| 20 |
| 20 |
| 20 |
+----+
4 rows in set (0.00 sec)
mysql> select distinct20 from stu_test;
+----+
| 20 |
+----+
| 20 |
+----+
1 row in set (0.00 sec)
mysql> select xingming,(age+dept) from stu_test;
+----------+------------+
| xingming | (age+dept) |
+----------+------------+
| laowang | 28 |
| huasheng | 23 |
| dadou | 20 |
| dadou | 20 |
+----------+------------+
4 rows in set, 3 warnings (0.01 sec)
mysql> selectxingming,(age+dept)+10 from stu_test; #在上面的基础上加10
+----------+---------------+
| xingming | (age+dept)+10 |
+----------+---------------+
| laowang | 38 |
| huasheng | 33 |
| dadou | 30 |
| dadou | 30 |
+----------+---------------+
4 rows in set, 3 warnings (0.00 sec)
小结：
select * from student where name='王五';
select name,english from student;
select distinct english from student;
select name,(chinese+english+math) fromstudent;
select name,(chinese+english+math)+10 fromstudent;
select name as 姓名,(chinese+english+math)+10 as 总分 from student; //别名
select name 姓名,(chinese+english+math)+10 总分 from student;
select * from student whereenglish>'90';
select name from student where(chinese+english+math)>200;
select name from student where(chinese+english+math)> '200' //这里用单引号也是可以的
select name from student whereenglish>80 and english<90;
select name from student where Englishbetween 80 and 90; //这句跟上面那句是一样的
select * from student where mathin(89,90,91);
4.2模糊查询
使用like 加上百分号来匹配
select * from student where name like '李_'; （2个字符）
select * from student where name like '李%'; (2个字符以上)
4.3排序查询
order by 排序查询
select name,math from student order by math; #默认是升序排序
select name 姓名,(chinese+english+math) 总分 from student order by (chinese+english+math) desc; #desc参数是降序
select name 姓名,(chinese+english+math) 总分 from student order by 总分 desc;
select * from student where name like '李%' order by (chinese+english+math) desc;
4.4统计数据
我们有时候要看一个表里面有多少条数据，需要统计
select count(name) from student; ##查看name字段有多少条记录
select count(*) from student;
select count(*) from student where(chinese+english+math)>250;
4.5数据求和
求和
select sum(chinese),sum(english),sum(math) fromstudent;
select sum(chinese+english+math) from student;
4.6求平均
select avg(chinese) from student;
select avg(chinese+math+english) from student;
转载于:https://blog.51cto.com/sgk2011/1844109
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