How to implement database addition, deletion, modification and query operations in PHP

Adding, deleting, modifying, and querying the database is one of the basic operations of Web development. As a powerful Web back-end development language, PHP also has a very convenient way to operate the database. In this article, we will introduce how to use PHP to implement add, delete, modify and query operations in the database.

1. Connect to the database

In PHP, connecting to the database is an essential step. We need to use the mysqli function provided by PHP, which can conveniently operate the MySQL database.

The following is a sample code for connecting to a MySQL database:

<?php
    $db_host="localhost";  //数据库服务器名称
    $db_user="root";       //连接数据库用户名
    $db_pass="";           //连接数据库密码
    $db_name="test";       //数据库名称

    $mysqli=new mysqli($db_host,$db_user,$db_pass,$db_name);

    if(mysqli_connect_errno()){
        echo "连接MySQL失败: " . mysqli_connect_error();
        exit();
    }
?>

The above code is used to connect to a database named test. Among them, $db_host represents the name of the database server, $db_user represents the user name to connect to the database, $db_pass represents the password of the user, and $db_name represents the name of the database to be connected. If the connection fails, the mysqli_connect_errno function will return an error code, and we can obtain specific error information through the mysqli_connect_error() function.

2. Insert data

Adding data to the database is a common task. The following is sample code for adding a piece of data to a database named test:

<?php
    $mysqli->query("INSERT INTO user (username, password, age) VALUES ('小明','123456',18)");
?>

In the above code, we insert a piece of data into the user table. Note that the data needs to be enclosed in single or double quotes. Also, if you have an older version of PHP, you can also use the mysql_query function, which has the same functionality.

3. Delete data

To delete specific data in the database, use the DELETE statement. The following is sample code for deleting records with username value "Xiao Ming" from a database named test:

<?php
    $mysqli->query("DELETE FROM user WHERE username='小明'");
?>

In this example, we use the DELETE statement to delete records from the user table. Note that we use the WHERE clause to specify the records to be deleted. If you have an older version of PHP, you can also use the mysql_query function, which has the same functionality.

4. Update data

Modifying data in the database is a very common operation. Update statements are used to update data in database tables. The following is sample code for modifying the age value of username "Xiaohong" in a database named test:

<?php
    $mysqli->query("UPDATE user SET age=20 WHERE username='小红'");
?>

In this example, we use the UPDATE statement to update a certain value in the user table Record. We use the SET clause to specify the fields and values ​​to be modified. Note that the WHERE clause is used to specify the records to be updated. If you have an older version of PHP, you can also use the mysql_query function, which has the same functionality.

5. Query data

You can use the SELECT statement to retrieve data from the database. Below is the sample code to retrieve all other information in the test database:

<?php
    $result=$mysqli->query("SELECT * FROM user");

    while($row = mysqli_fetch_array($result)){
        echo $row['username'];
        echo " ";
        echo $row['age'];
        echo "<br />";
    }
?>

In this example, we use the SELECT statement to retrieve all the records from the user table and output them. The mysqli_fetch_array() function is used to retrieve each row, place it in an array, and then output it to the browser. If you have an older version of PHP, you can also use the mysql_query function, which has the same functionality.

Summary

This article introduces the addition, deletion, modification and query operations when using PHP to operate the MySQL database. You can easily connect to a MySQL database using mysqli functions and use SQL statements to add, delete, update, and query data. Using these sample codes, you can easily start using PHP to access your MySQL database.

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