MySql踩坑记录之查询条件无法查出null字段

字段EDD_CTGY值全部为null
使用语句：select ID, EDD_CTGY from t_test where EDD_CTGY <> ‘abc’;
结果为无记录

解决方式1：select ID, EDD_CTGY from t_test where EDD_CTGY <> ‘abc’ or EDD_CTGY is null;
解决方式2：select ID, EDD_CTGY from t_test where ifnull(EDD_CTGY, ‘’) <> ‘abc’;