写了一个简单的登录验证，居然搞了半天，还各种查mysqli num_rows，还以为是num_rows出问题，后面在如图所示后面加了条是否存在结果集的判断，运行下，错误结果出来了，就明白是$sql有问题。
错误显示：You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '$sql' at line 11064
单引号加$sql,我也是醉了...，去掉单引号，OK！
转载于:https://blog.51cto.com/7080696/1886438