php怎么连接数据库,然后输出数据？给个简单的案例

给个案例，项目需要

PHP Data Objects

1. <?php
   
2. $servername = "localhost";
   
3. $username = "username";
   
4. $password = "password";
   
5. $dbname = "myDB";
   
6. 
   
7. try {
   
8.     $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
   
9.     // 设置PDO错误模式为异常
   
10.     $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    
11.     echo "连接成功";
    
12. }
    
13. catch(PDOException $e)
    
14. {
    
15.     echo "连接失败: " . $e->getMessage();
    
16. }
    
17. 
    
18. // 查询
    
19. $sql = "SELECT id, firstname, lastname FROM MyGuests";
    
20. foreach ($conn->query($sql) as $row) {
    
21.     print $row['id'] . "\t";
    
22.     print $row['firstname'] . "\t";
    
23.     print $row['lastname'] . "\n";
    
24. }
    
25. 
    
26. $conn = null;
    
27. ?>

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连接数据库：使用mysqli扩展。

1. $conn = new mysqli("localhost", "username", "password", "database");
   
2. if ($conn->connect_error) {
   
3.     die("连接失败: " . $conn->connect_error);
   
4. }

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查询数据：使用SQL语句。

1. $result = $conn->query("SELECT * FROM table_name");

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输出数据：遍历结果并打印。

1. if ($result->num_rows > 0) {
   
2.     while($row = $result->fetch_assoc()) {
   
3.         echo "id: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
   
4.     }
   
5. } else {
   
6.     echo "0 结果";
   
7. }
   
8. $conn->close();

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使用PDO（PHP Data Objects）来连接数据库。PDO提供了一个统一的接口来访问多种数据库

1. try {
   
2.     $pdo = new PDO("mysql:host=localhost;dbname=database", "username", "password");
   
3.     $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
   
4. 
   
5.     $stmt = $pdo->query("SELECT * FROM table_name");
   
6.     while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
   
7.         echo $row['name'] . "<br />";
   
8.     }
   
9. } catch(PDOException $e) {
   
10.     echo "连接失败: " . $e->getMessage();
    
11. }

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确保你的服务器上安装了MySQL和PHP

1. $conn = mysqli_connect("localhost", "username", "password", "database");
   
2. if (!$conn) {
   
3.     die("连接错误: " . mysqli_connect_error());
   
4. }
   
5. $sql = "SELECT id, name FROM table_name";
   
6. $result = mysqli_query($conn, $sql);
   
7. if (mysqli_num_rows($result) > 0) {
   
8.     while($row = mysqli_fetch_assoc($result)) {
   
9.         echo "id: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
   
10.     }
    
11. } else {
    
12.     echo "0 结果";
    
13. }
    
14. mysqli_close($conn);

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避免SQL注入是关键。使用预处理语句和参数化查询可以大大提高安全性‘

1. $conn = new mysqli("localhost", "username", "password", "database");
   
2. if ($conn->connect_error) {
   
3.     die("连接失败: " . $conn->connect_error);
   
4. }
   
5. $stmt = $conn->prepare("SELECT id, name FROM table_name WHERE id = ?");
   
6. $stmt->bind_param("i", $id);
   
7. $id = 1;
   
8. $stmt->execute();
   
9. $result = $stmt->get_result();
   
10. if ($result->num_rows > 0) {
    
11.     while($row = $result->fetch_assoc()) {
    
12.         echo "id: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
    
13.     }
    
14. } else {
    
15.     echo "0 结果";
    
16. }
    
17. $stmt->close();
    
18. $conn->close();

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PDO或mysqli

1. <?php
   
2. $servername = "localhost";
   
3. $username = "username";
   
4. $password = "password";
   
5. $dbname = "myDB";
   
6. 
   
7. // 创建连接
   
8. $conn = new mysqli($servername, $username, $password, $dbname);
   
9. 
   
10. // 检查连接
    
11. if ($conn->connect_error) {
    
12.     die("连接失败: " . $conn->connect_error);
    
13. }
    
14. 
    
15. $sql = "SELECT id, firstname, lastname FROM MyGuests";
    
16. $result = $conn->query($sql);
    
17. 
    
18. if ($result->num_rows > 0) {
    
19.     // 输出数据
    
20.     while($row = $result->fetch_assoc()) {
    
21.         echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    
22.     }
    
23. } else {
    
24.     echo "0 结果";
    
25. }
    
26. $conn->close();
    
27. ?>

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