Think/Model.php
public function execute($sql)
    {
        $sql = $this->parseSql($sql);

        return $this->db->execute($sql);
    }
public function execute($sql)
    {
        $sql = $this->parseSql($sql);

        return $this->db->execute($sql);
    }
执行SQL语句
@param string $sql SQL指令

@return false|int