ADO数据库异常

Question

EvaraintTypeCastError with message"  'coun't not convert varaint of( Null) into type(String)                                                                                                                                           
数据库是：SQL Server， 用ODBC连接。                                             
用的是 ADOTable                                                                 
                                                                                
每次一开始运行的时候就有这个错误。                                              
                                                                                
各位大侠怎么回事呀？？？                                                        
小弟 不胜感激！！

Answer 1

把出错的那句话用,用FieldByName('..').AsString强制转换

Answer 2

谢谢，问题找到了，是我的数据库的外键设计的有问题。不过还是谢谢你，让我知道了调试这个问题。
得分,
zen me gei fen ya