楼主,空值和空字符串是不同的概念
select depid, depname from deptable where parentdepid =''
是查询parentdepid为空字符串的
select depid, depname from deptable where parentdepid IS NULL
才是查询空值
select depid, depname from deptable where parentdepid =''
是查询parentdepid为空字符串的
select depid, depname from deptable where parentdepid IS NULL
才是查询空值
如果查非空,就用is not null
这个句子是正确的谢谢大家结了