SELECT DISTINCT t.id FROM MyClass t
 WHERE .....
 ORDER BY (a + b) DESC

Criteria criteria = getSession().createCriteria(MyClass.class);
criteria.setProjection(Projections.distinct(Projections.id()));
 
// Some custom dynamic conditions
criteria.add(Restrictions.gt("createdDate", afterDate));
criteria.add(Restrictions.in("state", approvedStates));
criteria.add(Restrictions.isNull("deletedDate"));
if (includedCategories != null || excludedCategories != null) {
    Criteria categoryCriteria = criteria.createCriteria("category");
    if (includedCategories != null) {
        for (String categoryPrefix : includedCategories) {
            categoryCriteria.add(Restrictions.like("path", categoryPrefix + "%"));
        }
    }
    if (excludedCategories != null) {
        for (String categoryPrefix : excludedCategories) {
            categoryCriteria.add(Restrictions.not(Restrictions.like("path", categoryPrefix + "%")));
        }
    }
}
 
criteria.add(Restrictions.sqlRestriction("(a + b) > 1"));
 
// Custom ordering by some SQL formula/expression
criteria.addOrder(Order.desc("a + b"));
 
return criteria.list();

package ro.tremend.util.hibernate;
 
import org.hibernate.criterion.Order;
import org.hibernate.criterion.CriteriaQuery;
import org.hibernate.Criteria;
import org.hibernate.HibernateException;
 
/**
 * Extends {@link org.hibernate.criterion.Order} to allow ordering by an SQL formula passed by the user.
 * Is simply appends the <code>sqlFormula</code> passed by the user to the resulting SQL query, without any verification.
 * @author Sorin Postelnicu
 * @since Jun 10, 2008
 */
public class OrderBySqlFormula extends Order {
    private String sqlFormula;
 
    /**
     * Constructor for Order.
     * @param sqlFormula an SQL formula that will be appended to the resulting SQL query
     */
    protected OrderBySqlFormula(String sqlFormula) {
        super(sqlFormula, true);
        this.sqlFormula = sqlFormula;
    }
 
    public String toString() {
        return sqlFormula;
    }
 
    public String toSqlString(Criteria criteria, CriteriaQuery criteriaQuery) throws HibernateException {
        return sqlFormula;
    }
 
    /**
     * Custom order
     *
     * @param sqlFormula an SQL formula that will be appended to the resulting SQL query
     * @return Order
     */
    public static Order sqlFormula(String sqlFormula) {
        return new OrderBySqlFormula(sqlFormula);
    }
}

        criteria.addOrder(OrderBySqlFormula.sqlFormula("(a + b) desc"));