列名无效是怎么回事

[htt9931]

我在vb中编程
Dim rs As New ADODB.Recordset
dim cn as new adodb.connection
dim nusername as string
cn 连接成功后

SQLstr = "select * from biao where Username=" & nusername

rs.Open SQLstr, cn

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当执行到rs.open时，错误提示为列名无效
而当sql语句在sql server 2000 的查询分析器中执行时无误
这是怎么回事？

[htt9931]

列名username在数据库中的数据类型为varchar（50）

[CrazyFor]

cn 连接成功后

SQLstr = "select * from biao where Username='" & nusername &"'"

rs.Open SQLstr, cn

[愉快的登山者]

SQLstr = "select * from biao where Username='" & nusername & "'"

rs.Open SQLstr, cn