How to connect to and query the database with PHP

PHP is a scripting language widely used in Web development. Its extensive open source and versatility make it the first choice for developing Web applications. In Web development, connecting to the database and querying the database are very basic operations. Therefore, this article will explain how to connect to the database and use PHP to query the database.

1. Connect to the database

To connect to the database in PHP, you need two parameters, one is the database address, and the other is the database account and password. Common database types include MySQL, PostgreSQL, etc., and different database connection APIs are also different. The following is an example of using MySQL database connection:

$host = "localhost"; // 数据库地址
$user = "username"; // 数据库用户名
$password = "password"; // 数据库密码
$dbname = "mydb"; // 数据库名

$con = mysqli_connect($host, $user, $password, $dbname); // 建立数据库连接
if (!$con) { // 判断是否连接成功
  die("连接失败：" . mysqli_connect_error()); // 连接失败，输出错误信息
}
echo "连接成功"; // 连接成功，输出成功信息
mysqli_close($con); // 关闭数据库连接

2. Query the database

After successfully connecting to the database , we can start querying the data in the database. PHP mainly has the following query operation functions:

1. mysqli_query() function

mysqli_query() function is used to perform query operations on the database. Can execute SELECT statements, INSERT, UPDATE, and DELETE operations.

$sql = "SELECT * FROM mydb WHERE id=1"; // 查询语句
$res = mysqli_query($con, $sql); // 执行查询操作
if (mysqli_num_rows($res) > 0) { // 判断是否有查询结果
  while ($row = mysqli_fetch_assoc($res)) { // 循环获取查询结果的每一行数据
    echo "ID: " . $row["id"] . " - Name: " . $row["name"] . " - Age: " . $row["age"] . "<br>"; // 输出每一行数据
  }
} else {
  echo "没有查询结果"; // 没有查询结果，输出提示信息
}
mysqli_close($con); // 关闭数据库连接

2. mysqli_fetch_array() function

mysqli_fetch_array() function is used to get the first row of data from the result set and return it in the form of an array. Mainly used for SELECT operations.

$sql = "SELECT * FROM mydb"; // 查询语句
$res = mysqli_query($con, $sql); // 执行查询操作
if (mysqli_num_rows($res) > 0) { // 判断是否有查询结果
  while ($row = mysqli_fetch_array($res)) { // 循环获取查询结果的每一行数据（使用mysqli_fetch_array方式）
    echo "ID: " . $row["id"] . " - Name: " . $row["name"] . " - Age: " . $row["age"] . "<br>"; // 输出每一行数据
  }
} else {
  echo "没有查询结果"; // 没有查询结果，输出提示信息
}
mysqli_close($con); // 关闭数据库连接

3. mysqli_num_rows() function

mysqli_num_rows() function is used to get the number of rows in the query result set.

$sql = "SELECT * FROM mydb"; // 查询语句
$res = mysqli_query($con, $sql); // 执行查询操作
$num = mysqli_num_rows($res); // 获取查询结果集的行数
echo "查询结果总共有：" . $num . " 行"; // 输出查询结果总共的行数
mysqli_close($con); // 关闭数据库连接

4. mysqli_affected_rows() function

mysqli_affected_rows() function is used to obtain the number of rows affected by INSERT, UPDATE, DELETE and other operations.

$sql = "UPDATE mydb SET name='张三' WHERE id=1"; // 修改语句
$res = mysqli_query($con, $sql); // 执行UPDATE语句
$num = mysqli_affected_rows($con); // 获取修改影响的行数
echo $num . " 行记录被修改"; // 输出修改影响的行数
mysqli_close($con); // 关闭数据库连接

3. Summary

In this article, we introduced how to connect to the database and query the database through PHP. First, by using the mysqli_connect() function, we can establish a connection to the MySQL database. We then covered how to use the mysqli_query() function to issue SQL statements and process result sets. Finally, we introduced some of the main query data manipulation functions and how to obtain the number of rows and the number of affected rows in the query result set.

I hope you can understand the basic operations of connecting to the database and querying the database with PHP through this article. Of course, this article is only an entry-level article. PHP also has more powerful database operation functions. Interested students can learn in depth on their own.

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