What is the difference between mysql and mysqli in php

Difference: mysqli is a permanent connection function, while mysql is a non-persistent connection function. Mysql will open a connection process every time it is connected; mysqli always uses the same connection process, which can greatly reduce the pressure on the server side.

The operating environment of this tutorial: windows7 system, PHP7.1&&mysql8 version, DELL G3 computer

1. mysql and Related concepts of mysqli:

1. Mysql and mysqli are both function sets in PHP and have little connection with the mysql database.

2. Before the php5 version, the mysql function of php was generally used to drive the mysql database. For example, the mysql_query() function is process-oriented. 3. After the php5 version, the mysqli function has been added. In a sense, it is an enhanced version of the mysql system function, which is more stable, efficient and secure. Corresponding to mysql_query() is mysqli_query(), which is object-oriented and uses objects to operate and drive the mysql database

2. The difference between mysql and mysqli:

mysqli is a permanent connection function, while mysql is a non-persistent connection function.

mysql connection: Every time it is used for the second time, a new process will be reopened.

mysqli connection: always use the same process.

Benefits: This can greatly reduce the pressure on the server side.

Mysqli encapsulates some advanced operations such as transactions, and also encapsulates many available methods in the DB operation process.

3. Usage of mysql and mysqli:

1: mysql (process mode):

$conn = mysql_connect('localhost', 'user', 'password');　//连接mysql数据库　　mysql_select_db('data_base'); 
 //选择数据库　　
 $result = mysql_query('select * from data_base');//第二个可选参数，指定打开的连接　　
 $row = mysql_fetch_row( $result ) ) //只取一行数据　　
 echo $row[0]; //输出第一个字段的值　　

PS: mysqli operates in a procedural manner. Some functions must specify resources, such as mysqli_query (resource identifier, SQL statement), and the parameter of the resource identifier is placed in front, while mysql_query (SQL statement, 'resource identifier' ) is optional, and the default value is the last opened connection or resource.

2. mysqli (object mode):

$conn = new mysqli('localhost', 'user', 'password','data_base');　　//要使用new操作符，最后一个参数是直接指定数据库　　//假如构造时候不指定，那下一句需要$conn -> select_db('data_base')实现　　$result = 
 $conn -> query( 'select * from data_base' );　　
 $row = result -> fetch_row(); //取一行数据　　
 echo row[0]; //输出第一个字段的值

Use new mysqli('localhost', usenamer', 'password', 'databasename'); An error will be reported and the prompt is as follows:

Fatal error: Class 'mysqli' not found in ...

Generally, mysqli is not enabled because the mysqli class is not enabled by default. Under win, you need to change php.ini and remove the ";" in front of php_mysqli.dll. Under Linux Mysqli needs to be compiled into it.

4. mysql_connect() and mysqli_connect()

1. Using mysqli, you can pass the database name as a parameter to mysqli_connect() function, can also be passed to the constructor of mysqli;

2. If the mysqli_query() or mysqli object query query() method is called, the connection identifier is required.

Recommended learning: "PHP Video Tutorial"

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