这是网上找的sqldbhelper ,如文中的数据库连接字符串中的“A”,"B","C" 能不能用变量代替？程式调用这个类时才去选择调用那个数据库。谢谢！！
Imports System.Data
Imports System.Data.SqlClient

''' <summary>
''' 自定义访问通用类
''' </summary>
Public Class SqlDbHelper

Private connectionString As String = System.Configuration.ConfigurationManager.ConnectionStrings("A").ConnectionString
Private connectionStringA As String = System.Configuration.ConfigurationManager.ConnectionStrings("B").ConnectionString
Private connectionStringB As String = System.Configuration.ConfigurationManager.ConnectionStrings("C").ConnectionString

''' <summary>
''' 构造函数
''' </summary>
Public Sub New()
End Sub
''' <summary>
''' ExecuteNonQuery操作，对数据库进行 增、删、改 操作(（1）
''' </summary>
''' <param name="sql">要执行的SQL语句 </param>
''' <returns> </returns>
Public Function ExecuteNonQuery(ByVal sql As String) As Integer
Return ExecuteNonQuery(sql, CommandType.Text, Nothing)
End Function
''' <summary>
''' ExecuteNonQuery操作，对数据库进行 增、删、改 操作（2）
''' </summary>
''' <param name="sql">要执行的SQL语句 </param>
''' <param name="commandType">要执行的查询类型（存储过程、SQL文本） </param>
''' <returns> </returns>
Public Function ExecuteNonQuery(ByVal sql As String, ByVal commandType As CommandType) As Integer
Return ExecuteNonQuery(sql, commandType, Nothing)


[解决办法]