This is a proof of concept of a database class for PHP

cherry-db-2.php

<?
        class MySQLAdapter {
		private $sql;

		public function run_query()
		{
			die($this->sql());
		}

		public function sql($sql = null)
		{
			if ($sql == null) return $this->sql;

			if ($this->sql != null) $this->sql .= " ".$sql;
			else $this->sql = $sql;
		}

		public function select($columns)
		{
			$this->sql("SELECT $columns");

			return $this;
		}

		public function where($arguments = array())
		{
			$end_sql = 'WHERE 1=1';

			foreach ($arguments as $column => $value)
			{
				$end_sql .= " AND $column = $value";
			}

			$this->sql($end_sql);

			return $this;
		}

		public function order_by($column, $order = 'DESC')
		{
			$this->sql("ORDER BY $column $order");
		}
	}

	class Database {
		private $adapter;
		private $id_column = 'id';

		public function __construct($adapter)
		{
			$this->adapter = $adapter;
		}

		public function find($id)
		{
			$this->adapter->select('user_id')->where(array($this->id_column => $id))->order_by('id', 'DESC');

			return $this->adapter->run_query();
		}

	}

	$db = new Database( new MySQLAdapter );

	$db->find(5);