How to use database query and result filtering functions in PHP to perform data condition query and result statistics?

How to use database query and result filtering functions in PHP to perform data condition query and result statistics?

In PHP, we often need to obtain data under specific conditions through database queries, and perform statistical analysis based on the query results. In order to achieve this goal, we can use PHP's database query function and result filtering function to achieve this.

First, we need to connect to the database and select the database to operate. Database extensions such as mysqli or PDO can be used to connect to the database. The following is a sample code that uses the mysqli extension to connect to a MySQL database:

<?php
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "test";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

Next, we can use SQL statements to query data. Common query statements include SELECT statements, UPDATE statements, DELETE statements, etc. The following is a sample code that uses the SELECT statement for data query:

$sql = "SELECT * FROM users WHERE age > 18"; // 查询年龄大于18岁的用户
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "姓名: " . $row["name"]. " - 年龄: " . $row["age"]. "<br>";
    }
} else {
    echo "没有找到符合条件的数据";
}

In the above sample code, we use the WHERE keyword to set conditions and only return user data older than 18 years old. By traversing the result set through a while loop, we can obtain each piece of data that meets the conditions and process it.

In addition to conditional query, we can also use the result filtering function to perform statistical analysis on the query results. For example, we can use the COUNT function to count the number of records that meet the criteria. The following is a sample code that uses the COUNT function to count the number of users:

$sql = "SELECT COUNT(*) AS total FROM users WHERE age > 18"; // 统计年龄大于18岁的用户数量
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    $row = $result->fetch_assoc();
    echo "年龄大于18岁的用户数量为: " . $row["total"];
} else {
    echo "没有找到符合条件的数据";
}

In the above sample code, we use COUNT(*) to count the number of records that meet the criteria, and name the result field total. Get the total number of records in the result set through the fetch_assoc function and output it.

To sum up, by using PHP's database query function and result filtering function, we can easily perform data condition query and result statistics. Using appropriate SQL statements and functions, we can quickly obtain the required data and process it flexibly. I hope this article helps you use database query and result filtering functions in PHP.

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