com.microsoft.sqlserver.jdbc.SQLServerException: '=' 附近有语法错误。求大神指点迷津！

public class WorkDAOImpl  implements WorkDAO {



	protected Connection con;  //数据库连接

	protected PreparedStatement pre;  //实例

	protected ResultSet res;  //结果集

	

	public List<CustomerInfo> getAllList(  int addTime ) {

		

		List<CustomerInfo> list = new ArrayList<CustomerInfo>();

		con = DBCon.getConnection();

		try {

			String sql="select a.*  , b.condition_name  from  customer_info a ,customer_condition  b  " +

			"where a.condition_id=b.condition_id   and   a.is_used='1' ";

			if(addTime == 0 ){

				sql += " select datediff(day,birth_day,getDate())=0";

				

			} else	if(addTime != 0 ){

				sql += " select datediff(day,birth_day,getDate())>=0 and datediff(day,birth_day,getDate())<='"+addTime+"' ";

				

			}

			pre = con.prepareStatement(sql);

			res = pre.executeQuery();             //报错内容中提到这行   也不知道为什么

			while (res.next()) {

				CustomerInfo customerInfo = new CustomerInfo();

				

				customerInfo.setCustomerId(res.getInt("customer_id"));

				customerInfo.setCustomerName(res.getString("customer_name"));

				customerInfo.setCustomerBirthday(res.getString("birth_day"));

				customerInfo.setCustomerMobile(res.getString("customer_mobile"));

				customerInfo.setConditionId(res.getInt("condition_id"));

				customerInfo.setCustomerCondition(res.getString("condition_name"));

				customerInfo.setIsUsed(res.getString("is_used"));

				

	

				list.add(customerInfo);

				}

		} catch (SQLException e) {

			e.printStackTrace();

		}finally{

		    DBCon.closeAll(con,pre,res);	

		}

		return list;

		}