1.不为空
select * from table where id <> "";
select * from table where id != "";
select * from table where id not is null
2.为空
select * from table where id ="";
select * from table where isNull(id);
select * from table where id is null
具体情况具体分析,如果字段是char或者varchar类型的,使用id=""可以的;
如果字段是int类型的,使用isNull会好些。