php中怎么使用pdo查询数据

在使用PDO查询数据时，可以按照以下步骤进行操作：

1. 连接到数据库：

$servername = "localhost";
    
$username = "root";
    
$password = "";
    
$dbname = "database_name";


try {
    
    $conn = new PDO("mysql:host=$servername;
    dbname=$dbname", $username, $password);
    
    $conn->
    setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    
    echo "Connected successfully";

}
 catch(PDOException $e) {
    
    echo "Connection failed: " . $e->
    getMessage();

}
    

1. 编写SQL查询语句：

$sql = "SELECT * FROM table_name";
    

1. 准备并执行查询语句：

$stmt = $conn->
    prepare($sql);
    
$stmt->
    execute();
    

1. 获取查询结果：

$result = $stmt->
    fetchAll(PDO::FETCH_ASSOC);

1. 处理查询结果：

foreach($result as $row) {
    
    echo $row['column_name'];

}
    

完整的示例代码如下：

$servername = "localhost";
    
$username = "root";
    
$password = "";
    
$dbname = "database_name";


try {
    
    $conn = new PDO("mysql:host=$servername;
    dbname=$dbname", $username, $password);
    
    $conn->
    setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    
    echo "Connected successfully";
    

    $sql = "SELECT * FROM table_name";
    
    $stmt = $conn->
    prepare($sql);
    
    $stmt->
    execute();
    
    $result = $stmt->
    fetchAll(PDO::FETCH_ASSOC);


    foreach($result as $row) {
    
        echo $row['column_name'];

    }

}
 catch(PDOException $e) {
    
    echo "Connection failed: " . $e->
    getMessage();

}
    

注意替换$servername、$username、$password和$dbname为实际的数据库连接信息。同时，将table_name和column_name替换为实际的表名和列名。

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