从程序中构造sql语句执行时可用，防止多重判断
sb.Append( ” AND( 1=2 ” );
if (chkFilter.Items[0].Selected)
{
sb.Append(” OR ADSource=””);
}
if (chkFilter.Items[1].Selected)
{
sb.Append(” OR SearchKey=””);
}
if (chkFilter.Items[2].Selected)
{
sb.Append(” OR WebSource=””);
}
sb.Append( ” )” );