where表与字段都是变量 VB

请高手帮忙解决下，VB2010-where 表与字段都是变量，我的数字型可，但字符型报错，请高手更正
Dim ConnString As String = "Data Source=030PEL;Initial Catalog=hcrm;Persist Security Info=True;User ID=sa;Password=123454"
Dim dat As New SqlConnection(ConnString)
Dim sqltxt As String = " select * from " + tab + " where " + ziduang + " = " + where
MsgBox(sqltxt)
Dim sqlconn As New SqlCommand(sqltxt, dat) '定义sqlCommand

Dim da As New SqlDataAdapter(sqlconn) '定义sqldataadapter并于sqlcommand连接

Dim ds As New DataSet
Dim userReader As SqlDataReader '定义sqldatareader

Try
dat.Open() '打开连接

userReader = sqlconn.ExecuteReader '生成sqldatareader

userReader.Read() '读取数据

userReader.Close() '关闭阅读

da.Fill(ds, tab)
dataview.DataSource = ds.Tables(tab)
Catch ex As Exception
MsgBox(ex.Message)
Finally
sqlconn.Dispose() ' 释放sqlCommand

End Try

            ![图片说明](https://img-ask.csdn.net/upload/201703/23/1490198626_666684.jpg)

ziduang这个是什么类型的？如果是字符型，where两侧要加上引号

字段也变量，有时是字符，有时是数字

终于解决了。感谢大家。。。