How to solve database connection error in PHP5.6 to PHP7.4 compatibility issue?

How to solve the database connection error in PHP5.6 to PHP7.4 compatibility issue?

As the PHP version is updated, there are compatibility issues from PHP5.6 to PHP7.4. One of the common problems is database connection errors. This article will describe how to solve this problem and give corresponding code examples.

In PHP5.6 and previous versions, we usually use the mysql extension to connect and operate the database. Starting from PHP7.0, the mysql extension has been deprecated and replaced by the mysqli extension and PDO extension. Therefore, when upgrading the code from PHP5.6 to PHP7.4, the database connection code needs to be modified.

First of all, if your code uses the mysql extension, you need to replace it with the mysqli extension. The code to modify the database connection is as follows:

// PHP5.6及之前版本的数据库连接代码
$conn = mysql_connect($servername, $username, $password);
mysql_select_db($dbname, $conn);

// 修改为PHP7.4的数据库连接代码
$conn = mysqli_connect($servername, $username, $password, $dbname);

In the mysqli extension, the connection function name becomes "mysqli_connect", and the database name needs to be passed in as the fourth parameter.

In addition, it should be noted that starting from PHP7.4, it is no longer supported to use "localhost" as the host name when connecting to the database. If you use "localhost" when connecting to the database, the connection will fail. The solution to this problem is to replace "localhost" with "127.0.0.1" as shown below:

// 使用"127.0.0.1"代替"localhost"连接数据库
$servername = "127.0.0.1";

Next, we need to modify the code that executes the SQL query. In PHP5.6 and previous versions, we usually use the "mysql_query" function to execute SQL queries. In PHP7.4, you need to use the "mysqli_query" function to execute queries. The modified code looks like this:

// PHP5.6及之前版本的SQL查询代码
$result = mysql_query($sql);

// 修改为PHP7.4的SQL查询代码
$result = mysqli_query($conn, $sql);

Similarly, the "mysql_query" function needs to be replaced with the "mysqli_query" function and the database connection is passed to the function as the first parameter.

In addition to the mysqli extension, the PDO extension is also a good choice for connecting and operating databases. If you are using PDO extension in your code, you need to modify the database connection code as follows:

// PHP5.6及之前版本的数据库连接代码
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);

// 修改为PHP7.4的数据库连接代码
$conn = new PDO("mysqli:host=$servername;dbname=$dbname", $username, $password);

In the PDO extension, the database connection method is achieved by instantiating the PDO class, in the parameters "mysql" needs to be replaced with "mysqli".

To summarize, to solve the database connection error in PHP5.6 to PHP7.4 compatibility issues, you first need to replace the mysql extension with the mysqli extension or PDO extension. And note that when connecting to the database, replace "localhost" with "127.0.0.1". Additionally, the code that executes the SQL query needs to be modified accordingly.

Through the above modifications, the code can be successfully upgraded from PHP5.6 to PHP7.4 and compatibility errors caused by database connections can be solved. I hope the content of this article can be helpful to you.

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