How to fill Gridview from two different database tables but the record is not duplicate in Grid

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C#

ASP.NET

I have a User privilege form,where i load grid from Administrator table,further i insert data from Grid view with a check box property in a new User table in database, it works perfectly. But in next condition I want to load grid from both of two tables, first User Table where the data is shown with check box checked true property, and the second Administrator table, where data is shown with check box checked false property.if u understand my question, so please help me.My Code is:

protected void CmdUserRights_Click(object sender, ImageClickEventArgs e) 
{
StrSql = "Select Name from Sys.tables";
        StrSql = StrSql + " Where Name='" + "User_" + CboUserId.Text + "'"; 
        DataSet rs = (DataSet)MethodClass.ConnectionToQuery(StrSql);

        if (rs.Tables[0].Rows.Count <= 0)
           {
            StrSql = "Select * from User_Administrator";
            StrSql = StrSql + " Order by serial_no asc";
            DataSet rs2 = (DataSet)MethodClass.ConnectionToQuery(StrSql);
            GvUserPrivilege.DataSource = rs2.Tables[0];
            GvUserPrivilege.DataBind();
            }
        else
        {
            StrSql = "Select * from " + "[User_" + CboUserId.Text + "]";
            StrSql = StrSql + " Order By serial_no asc ";
            DataSet rs4 = (DataSet)MethodClass.ConnectionToQuery(StrSql);
            if (rs4.Tables[0].Rows.Count > 0)
               {
                GvUserPrivilege.DataSource = rs4.Tables[0];
                GvUserPrivilege.DataBind();
                foreach (GridViewRow rows in GvUserPrivilege.Rows)
                  {
                   CheckBox ChkBoxRows = (CheckBox)rows.FindControl("chk");
                   ChkBoxRows.Checked = true;
                  }
               }
            else
               {
               }
            }
}