--创建数据库 create database school --打开数据库 use school --创建表 create table student ( id int, name varchar(20), sex char(2), age int, date datetime, info text, bak varchar(500) ) --查看表结构 exec sp_help student --修改、添加列(字段)
--创建数据库
create database school
--打开数据库
use school
--创建表
create table student
(
id int,
name varchar(20),
sex char(2),
age int,
date datetime,
info text,
bak varchar(500)
)
--查看表结构
exec sp_help student
--修改、添加列(字段)
alter table student
add tel varchar(20)
--删除列(字段)
alter table student
drop column bak
--属性修改
--修改列名(字段名)
exec sp_rename 'student.sex','sex2'
--修改类型
alter table student
alter column age char(20)
--删除表
drop table student
-------------------------------表(结构):--------------------------------------------
----创建表,查看表结构,修改(增加列、删除列、属性(如姓名、年龄),,删除表)
---数据的完整性:主键约束、唯一约束、检查性约束、默认约束、外键约束
create table biao
(
id int primary key,
name varchar(20),
sex char(2) check(sex='男' or sex='女'),
age int,
date datetime,
info text,
tel char(16) unique,
bak varchar(500) default '我是学生'
)
create table grade
(
id int not null,
name varchar(20),
sex char(2),
age int,
date datetime,
info text,
bak varchar(500)
)
alter table grade
add tel char(16)
---增加主键
alter table grade
add constraint aa primary key(id)
---添加唯一性约束
alter table grade
add constraint bb unique(tel)
---查看约束
exec sp_helpconstraint grade
---添加检查性约束
alter table grade
add constraint sex check(sex='男' or sex='女')
---添加默认约束
alter table grade
add constraint ccc default '我是好学生' for bak
---删除约束
alter table grade
drop constraint ccc
-----------------------------添加约束的格式------------------------------------------
---alter table 表名
---add constraint 约束名(别名(任意取)) 约束关键字
----作业题,7.28-----
create table shop_jb
(
id int primary key,
namel varchar(20),
spec varchar(20),
stock int,
price float,
datel datetime default '2010-7-6'
)
create table shop_yw
(
ywid int primary key,
name2 varchar(20),
sex char(2) check(sex='男' or sex='女'),
age int,
tel varchar(18) unique,
address varchar(20)
)
create table shop_xs
(
id int not null,
sale char(20),
quantity char(20),
date2 datetime default '2010-5-3',
ywid int
foreign key(id) references shop_jb,
foreign key(ywid) references shop_yw
)
例如:
修改表expert_info中的字段birth,允许其为空
>alter table expert_info change birth birth varchar(20) null;
1.增加一个字段(一列)
alter table table_name add column column_name type default value; type指该字段的类型,value指该字段的默认值
例如:alter table mybook add column publish_house varchar(10) default '';
2.更改一个字段名字(也可以改变类型和默认值)
alter table table_name change sorce_col_name dest_col_name type default value; source_col_name指原来的字段名称,dest_col_name
指改后的字段名称
例如:alter table Board_Info change IsMobile IsTelphone int(3) unsigned default 1;
3.改变一个字段的默认值
alter table table_name alter column_name set default value;
例如:alter table book alter flag set default '0';
4.改变一个字段的数据类型
alter table table_name change column column_name column_name type;
例如:alter table userinfo change column username username varchar(20);
5.向一个表中增加一个列做为主键
alter table table_name add column column_name type auto_increment PRIMARY KEY;
例如:alter table book add column id int(10) auto_increment PRIMARY KEY;
6.数据库某表的备份,在命令行中输入:
mysqldump -u root -p database_name table_name > bak_file_name
例如:mysqldump -u root -p f_info user_info > user_info.dat
7.导出数据
select_statment into outfile"dest_file";
例如:select cooperatecode,createtime from publish limit 10 into outfile"/home/mzc/temp/tempbad.txt";
8.导入数据
load data infile"file_name" into table table_name;
例如:load data infile"/home/mzc/temp/tempbad.txt" into table pad;
9.将两个表里的数据拼接后插入到另一个表里。下面的例子说明将t1表中的com2和t2表中的com1字段的值拼接后插入到tx表对应的
字段里。
例如:insert into tx select t1.com1,concat(t1.com2,t2.com1) from t1,t2;
10,删除字段
alter table form1 drop column 列名;
补充一个:
PHP操作MySQL对表增加一列
于已经建立好的数据库,在一个已经有字段的表内新加字段可用以下方法:
mysql_query(“ALTER TABLE `表名` ADD `字段` 字段类型”) or die(mysql_error());
例如,对表article添加字段keywords
代码:
代码如下

MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

MySQL is an open source relational database management system suitable for data storage, management, query and security. 1. It supports a variety of operating systems and is widely used in Web applications and other fields. 2. Through the client-server architecture and different storage engines, MySQL processes data efficiently. 3. Basic usage includes creating databases and tables, inserting, querying and updating data. 4. Advanced usage involves complex queries and stored procedures. 5. Common errors can be debugged through the EXPLAIN statement. 6. Performance optimization includes the rational use of indexes and optimized query statements.

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

InnoDB's lock mechanisms include shared locks, exclusive locks, intention locks, record locks, gap locks and next key locks. 1. Shared lock allows transactions to read data without preventing other transactions from reading. 2. Exclusive lock prevents other transactions from reading and modifying data. 3. Intention lock optimizes lock efficiency. 4. Record lock lock index record. 5. Gap lock locks index recording gap. 6. The next key lock is a combination of record lock and gap lock to ensure data consistency.

The main reasons for poor MySQL query performance include not using indexes, wrong execution plan selection by the query optimizer, unreasonable table design, excessive data volume and lock competition. 1. No index causes slow querying, and adding indexes can significantly improve performance. 2. Use the EXPLAIN command to analyze the query plan and find out the optimizer error. 3. Reconstructing the table structure and optimizing JOIN conditions can improve table design problems. 4. When the data volume is large, partitioning and table division strategies are adopted. 5. In a high concurrency environment, optimizing transactions and locking strategies can reduce lock competition.

In database optimization, indexing strategies should be selected according to query requirements: 1. When the query involves multiple columns and the order of conditions is fixed, use composite indexes; 2. When the query involves multiple columns but the order of conditions is not fixed, use multiple single-column indexes. Composite indexes are suitable for optimizing multi-column queries, while single-column indexes are suitable for single-column queries.

To optimize MySQL slow query, slowquerylog and performance_schema need to be used: 1. Enable slowquerylog and set thresholds to record slow query; 2. Use performance_schema to analyze query execution details, find out performance bottlenecks and optimize.

MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.


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