PHP connects to MySQL

PHP 5 and above are recommended to use the following method to connect to MySQL:

· MySQLi extension ("i" means improved)

· PDO (PHP Data Objects)

In the PHP Early Edition we use mysql extension. However, this extension has been deprecated since 2012, because a set of mysql functions have been deprecated

---

I should use MySQLi. Or PDO?

If you need a short answer, "use whichever you are comfortable with".

mysqli and PDO have their own advantages:

PDO is applied in 12 different databases, and MySQLI only targets MySQL database.

Therefore, if your project needs to be switched in a variety of databases, it is recommended to use PDO, so you only need to modify the connection string and the department inquiry statement. Use mysqli. If you have different databases, you need to rewrite all the

code, including query.

Both are object -oriented, but mysqli also provides the API interface.

Both support prepared statements. Prepared statements can prevent SQL injection and are very important for the security of web projects.

---

MySQLi and PDO connect to the MySQL instance

In this chapter and the following chapters, we will use the following three methods Any way to demonstrate how PHP operates MySQL:

· MySQLi (object-oriented)

· MySQLi (procedure-oriented)

· PDO

---

Connect MySQL

##Syntax

##mysql_connect (servername,username,password);

##Parameter Description

servername Optional. Specifies the server to connect to. The default is "localhost:3306".
## username	Optional. Specifies the username to log in with. The default value is the name of users with a server process.
# Password	. Standard the password used for login. The default is "".

Before we access the MySQL database, we need to connect to the database server first:

---

Instance (MySQLi - Object Oriented)

<?php
 $servername = "localhost";
 $username = "username";
 $password = "password";
 
 // 创建连接
 $conn = new mysqli($servername, $username, $password);
 
 // 检测连接
 if ($conn->connect_error) {
     die("连接失败: " . $conn->connect_error);
 }
 echo "连接成功";
 ?>

Note that $connect_error in the above object-oriented example was added in PHP 5.2.9 and 5.3.0. If you need to be compatible with earlier versions, please use the following code replacement:

//Detect connection
if (mysqli_connect_error()) {
die("Database connection failed: " . mysqli_connect_error());
}

---

Instance (MySQLi - procedure-oriented)

<?php
 $servername = "localhost";
 $username = "username";
 $password = "password";
 
 // 创建连接
 $conn = mysqli_connect($servername, $username, $password);
 
 // 检测连接
 if (!$conn) {
     die("Connection failed: " . mysqli_connect_error());
 }
 echo "连接成功";
 ?>

---

Instance (PDO)

<?php
 $servername = "localhost";
 $username = "username";
 $password = "password";
 
 try {
     $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
     echo "连接成功";
 }
 catch(PDOException $e)
 {
     echo $e->getMessage();
 }
 ?>

Note: In the above PDO In the example we have specified the database (myDB). PDO needs to set the database name during the connection process. If not specified, an exception will be thrown

---

Close the connection

The connection will be automatically closed after the script is executed. You can also use the following code to close the connection:

Instance (MySQLi - Object Oriented)

$conn->close ();

Instance (MySQLi - process-oriented)

##mysqli_close($conn);

Instance (PDO)

$conn = null;

---

Instance

In the following example, we store the database connection in a variable ($con). If the connection fails, the "die" part will be executed; if the connection is successful, the connection will be closed after the program is executed.

<?php
 header("Content-type:text/html;charset=utf-8");    //设置编码
 $con = mysqli_connect("localhost","root","root","test");
 if (!$con)
 {
     die('Could not connect: ' . mysqli_error());
 }
 else{
     echo "连接数据库成功";
 }
 // some code
 mysqli_close($con);
 
 ?>

The above code means to connect to a server named localhost, the user name is root, the password is root, and the test database is used; if the connection fails, execute the code in die

Program running result:

Connection to database successful