最开始我的使用是
select * from admin where (adminid like ‘‘ or adminid is null) or (adminpwd like ‘‘ or adminpwd is null);
但是无法实现所有条件为空时查询全部，后来突然明白我为什么要这样设置sql语句我可以拼接字符串啊
于是
String sql=“select * from admin”;
if(adminname!null){
sql+=“where adminname like ‘%参数%‘;
}else if(xxx){
sql+=xxx
}
selectsql（sql）；//调取查询语句