官方文档：https://docs.oracle.com/en/database/oracle/oracle-database/26/sqlrf/Nulls.html#GUID-C785FE74-5F9C-4F70-AC4B-CA5D3010162A

The database currently treats a character value with a length of zero as null. However, this may not continue to be true in future releases, and Oracle recommends that you do not treat empty strings the same as nulls.

空串就是null。

判断描述

任何以= 或 != 与Null判断结果为Unknown。

// wrapper.ne(BaseDeptDO::getDeptName, “”); 这行代码就是deptname !=‘’ deptname != Null 结果为unknown，无论库里什么值，都查不出来