SQLSERVER中主键重复输入的防范问题(100分)

const eKeyVol = 9729 ;<br>begin<br>////////////////<br>&nbsp; &nbsp; if(E is EDBEngineError) then<br>&nbsp; &nbsp; &nbsp; &nbsp; if(E as EDBEngineError).Errors[0].ErrorCode = &nbsp;eKeyVol then<br>&nbsp; &nbsp; &nbsp; &nbsp; begin<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Application.MessageBox('客户已存在！', '', MB_OK+MB_ICONINFORMATION);<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; query1.Cancel;<br>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; abort;<br>&nbsp; &nbsp; &nbsp; &nbsp; end;<br>////////////////<br><br>这个段代码在SQLSERVER中为什么不行?<br>行的代码谁有?