如何用php mysql类实现查询功能

要用PHP和MySQL类实现查询功能，首先需要创建一个MySQL连接，然后使用SQL查询语句执行查询，最后处理查询结果。以下是一个简单的示例：

1. 创建一个MySQL连接类（DatabaseConnection.php）：

<?php class DatabaseConnection {     private $host = 'localhost';     private $username = 'your_username';     private $password = 'your_password';     private $database = 'your_database';      public function __construct() {         $this->connection = new mysqli($this->host, $this->username, $this->password, $this->database);         if ($this->connection->connect_error) {             die("连接失败: " . $this->connection->connect_error);         }     }      public function closeConnection() {         $this->connection->close();     } } ?> 

2. 创建一个查询类（Query.php）：

<?php class Query {     private $connection;      public function __construct($connection) {         $this->connection = $connection;     }      public function select($table, $columns = "*", $condition = []) {         $sql = "SELECT " . implode(", ", $columns) . " FROM " . $table;          if (!empty($condition)) {             $sql .= " WHERE ";             $conditions = [];             foreach ($condition as $key => $value) {                 $conditions[] = $key . " = '" . $value . "'";             }             $sql .= implode(" AND ", $conditions);         }          $result = $this->connection->query($sql);         return $result;     } } ?> 

3. 在主文件中使用这两个类（index.php）：

<?php require_once 'DatabaseConnection.php'; require_once 'Query.php';  $db = new DatabaseConnection(); $query = new Query($db->connection);  // 查询示例 $table = 'users'; $columns = ['id', 'name', 'email']; $condition = ['id' => 1]; $result = $query->select($table, $columns, $condition);  if ($result->num_rows > 0) {     while($row = $result->fetch_assoc()) {         echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "<br>";     } } else {     echo "0 结果"; }  $db->closeConnection(); ?> 

这个示例展示了如何使用PHP和MySQL类实现基本的查询功能。你可以根据需要进行修改和扩展。