你了解哪些PHP常用的小程序代码段？

PHP常用的小程序代码段

1. 连接MySQL数据库

代码段

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn>connect_error) {
    die("Connection failed: " . $conn>connect_error);
}
echo "Connected successfully";
?>

2. 插入数据到MySQL数据库

代码段

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn>connect_error) {
    die("Connection failed: " . $conn>connect_error);
}
$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";
if ($conn>query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn>error;
}
$conn>close();
?>

3. 从MySQL数据库查询数据

代码段

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn>connect_error) {
    die("Connection failed: " . $conn>connect_error);
}
$sql = "SELECT id, firstname, lastname FROM MyGuests";
$result = $conn>query($sql);
if ($result>num_rows > 0) {
    // 输出数据
    while($row = $result>fetch_assoc()) {
        echo "id: " . $row["id"]. "  Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 results";
}
$conn>close();
?>

4. 更新MySQL数据库中的数据

代码段

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn>connect_error) {
    die("Connection failed: " . $conn>connect_error);
}
$sql = "UPDATE MyGuests SET lastname='Doe' WHERE id=2";
if ($conn>query($sql) === TRUE) {
    echo "Record updated successfully";
} else {
    echo "Error updating record: " . $conn>error;
}
$conn>close();
?>

5. 删除MySQL数据库中的数据

代码段

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);
// 检测连接
if ($conn>connect_error) {
    die("Connection failed: " . $conn>connect_error);
}
$sql = "DELETE FROM MyGuests WHERE id=3";
if ($conn>query($sql) === TRUE) {
    echo "Record deleted successfully";
} else {
    echo "Error deleting record: " . $conn>error;
}
$conn>close();
?>

相关问题与解答

问题1：如何在PHP中防止SQL注入？

回答：在PHP中防止SQL注入的常用方法是使用预处理语句（prepared statements）和绑定参数，预处理语句确保了SQL语句的结构在执行前已经固定，从而避免了恶意输入对数据库结构的影响，使用mysqli或PDO扩展来创建预处理语句。

问题2：如何优化数据库查询性能？

回答：优化数据库查询性能可以从多个方面入手，包括索引的使用、查询语句的优化、减少返回的数据量等，合理地设计数据库表结构，为经常需要查询的列添加索引可以显著提高查询效率，避免在查询中使用复杂的计算和函数，尽量简化查询逻辑，也是提升性能的有效方法。

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