在使用ResultSet时发生的错误：
ResultSet rs=st.executeQuery();
//直接rs.getString("Name") 会报错before start of result set
//要使用
while(rs.next()){
rs.get...;
}
//如果确定了rs里面只有一条数据可以不用循环，直接使用if（rs.next（））即可
if(rs.next()){
rs.get...;
}
百度得到：即使你十分确定能搜出记录，也不可以在没有rs.next()之前直接对rs进行取值。
这涉及到rs对象的存储方法。里面说白了就是指针。没next，指针根本没指向对应记录
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