php intval的取值范围：与操作系统相关，32位系统上为-2147483648到2147483647，64位系统上为-9223372036854775808到9223372036854775807。 
mysql int取值范围：与操作系统无关，为-2147483648到2881064151，无符号为0到4294967295。 
mysql bigint取值范围：与操作系统无关，为-9223372036854775808到9223372036854775807，无符号为0到18446744073709551615。 
所以下面的代码是错误的： 
复制代码 代码如下:
public function insert($data) 
{ 
if(isset($data['content'])&&!empty($data['content'])) 
{ 
$data_for_query['content'] = trim($data['content']); 
} 
else 
{ 
return false; 
} 
if(isset($data['user_id'])&&!empty($data['user_id'])) 
{ 
$data_for_query['user_id'] = intval($data['user_id']); 
} 
else 
{ 
return false; 
} 
$sql = "INSERT INTO `".$this->table_name."` (".$this->db->implodeToColumn(array_keys($data_for_query)).") VALUES (".$this->db->implodeToValues(array_values($data_for_query)).")"; 
$this->db->query($sql); 
$id = $this->db->lastInsertId(); 
if(empty($id)) 
{ 
return false; 
} 
else 
{ 
return $id; 
} 
}