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Data integrity　　Entity integrityEntity: A row in a table (a row of records) instead of an entityThe role of entity integrity: identifies each row of data that is not duplicated.Constraint type: PRIMARY KEY constraint, UNIQUE constraint, auto-Grow

I. Introduction of the Database1, the origin of the databaseWhat we've learned before is that data is stored in a file for permanent preservation, and there is no doubt that a file can only exist on a single machine, which poses many problems:(1)

1.SQL not NULL constraintThe NOT NULL constraint enforces that the column does not accept null values.A NOT NULL constraint forces a field to always contain a value. This means that if you do not add a value to the field, you cannot insert a new

Solve garbled problem:Chinese garbled is nothing more than coding format problem. MySQL is now UTF8 encoded by default.First: After Mysql_real_connect, the program is set to encode Mysql_set_character_set (MySQL, "UTF8"); "Someone might ask, is

MySQL TransactionMySQL transaction is mainly used to deal with large-scale and high-complexity data.For example, in a personnel management system, you delete a person, you need to delete the basic information of the person, but also to delete the

If you want to do a Java EE development on Linux, first build the Java EE development environment, including the JDK, Tomcat, Eclipse installation (this in a previous essay has explained in detail the Linux learning CentOS (vii)- CentOS under the

Optimizing GROUP BY statementsBy default, MySQL sorts all group by Col1,col2, ..... The method of querying is like specifying an order by Col1,col2 in a query .... If you explicitly include an ORDER BY clause that contains the same column, MySQL can

First, introduce the type of indexMySQL Common indexes are: Primary key index, unique index, normal index, full-text index, composite indexPRIMARY key (primary key index) ALTER TABLE ' table_name ' Add PRIMARY KEY (' column ') unique (unique index)

PHP and MySQL transaction processing$conn = mysql_connect (' localhost ', ' root ', ' root ') or Die ("Data connection error!!!");mysql_select_db (' Test ', $conn);mysql_query ("Set names ' GBK '"); Use GBK Chinese code;Start a

I. Automatic installation of MySQL via YumYum Install Mysql-server my-clientIi. initialization and related configurationAfter installing the MySQL database, you will find an extra mysqld service, and you can start the MySQL service by entering

This article mainly introduces you to what is the MySQL index? MySQL indexing is important for the efficient operation of MySQL, and indexing can greatly improve the retrieval speed of MySQL. For example, if the reasonable design and use of the

In a database table, indexing a field can greatly improve query speed. Suppose we create a mytable table:Copy CodeThe code is as follows: CREATE TABLE mytable (ID INT NOT NULL, username VARCHAR (+) not NULL);We randomly inserted 10,000 records,

Recently a lot of friends, are asking me how to connect navicate,mysql not connected. In fact, it is not recommended to do soFirewall shutdown project is very unsafe, but it is personal testing to do some of their own to the project is not

I. What is an index?Indexes are used to quickly look for records with specific values, and all MySQL indexes are saved as B-trees. If there is no index, MySQL must start scanning all records of the entire table from the first record until it finds a

The JOIN keyword is used in SQL to use table joins. There are several different types of table joins, which are supported by the mainstream database system (cross joins), Inner joins (INNER joins), outer joins (Outter joins), and Federated joins

Special Data type table constraint table connection index trigger security DB designAlter Table int Primary Key altertableint auto_increment;Special Data type enumSetTextBlobTIMESTAMPDefault ValueCreate TableUsers (IDinteger, namevarchar( -), likes

Introduction to installation and configuration of MySQL under Centos 6.4Our previous article has introduced the function is mainly used in the recent company's environmental structure construction, so today's article is mainly for the company's

Today, database operations are increasingly becoming a performance bottleneck for the entire application, which is especially noticeable for web applications. It's not just about the performance of the database that DBAs need to worry about, it's

There is usually a field in the table where create date is created, and other databases have the option of default values. MySQL also has a default value of timestamp, but in MySQL, not only is the insertion to be modified will also update the value

First, remove the original MySQLgrep mysql//This command will check if the MySQL database is already installed on the operating systemIf there is, we can unload it by RPM-E command or rpm-e--nodeps command.[[Email protected] ~]# RPM- normal Delete