Sql istinct）-功能

我用嵌套聚合函数解决了这个问题：

select sum(count(distinct u.lastname))
from Personel u 
group by u.firstname, u.lastname;

“u.lastname”必须是非空列

---

此语句在带有Oracle DB的HQL中工作。

如果结果计数为100000条记录，则此解决方案正常且性能良好？您只需要计数，还是在某处显示查询结果？我没有尝试过，但是用这种风格修改了上面的代码，并看到了结果。getMaxResults（）；我显示分页结果。例如，pagesize=10，我显示pagenumber=2，所有结果（按组）都是100000这是非常低效的这不是hql查询。在子选择中引用hql不支持hql。请再次检查

select count(*) 
from Personel u  
where u.lastname='azizkhani'

select u.lastname,count(*) 
from Personel u 
group by u.lastname;

select count(*) 
   from (
         select u.lastname,count(*) 
         from tbl_personel u 
         group  by u.lastname
    )

public <U> PagingResult<U> getAllGrid(String hql,Map<String, Object> params,PagingRequest searchOption);

   String hqlQuery = " select e from Personel e where 1<>2 and e.lastname=:lastname";

    HashMap<String, Object> params = new HashMap<String, Object>();
    params.put("lastname", 'azizkhani');


    return getAllGrid(hqlQuery, params, new PagingRequest( 0/*page*/, 10 /*size*/) );

public class PagingResult<T> {

    private int totalElements;

    @JsonProperty("rows")
    private List<T> items;

    public PagingResult() {

    }

    public PagingResult(int totalElements, List<T> items) {
        super();
        this.totalElements = totalElements;
        this.items = items;
    }


    public int getTotalElements() {
        return totalElements;
    }

    public void setTotalElements(int totalElements) {
        this.totalElements = totalElements;
    }


    public List<T> getItems() {
        return items;
    }

    public void setItems(List<T> items) {
        this.items = items;
    }

}

public <U> PagingResult<U> getAllGrid(String hql, Map<String, Object> params, PagingRequest searchOption) {
        Session session = getSession();
        applyDafaultAuthorizeFilter(session);


        Query query = session.createQuery(hql);
        if (searchOption != null) {
            if (searchOption.getSize() > 0) {
                query.setFirstResult(searchOption.getPage() * searchOption.getSize());
                query.setMaxResults(searchOption.getSize());
            }
        }
        if (params != null)
            HQLUtility.setQueryParameters(query, params);

        List<U> list = query.getResultList();

        Query countQuery = session.createQuery("select count(*) " + HQLUtility.retriveCountQueryFromHql(hql));

        if (params != null)
            HQLUtility.setQueryParameters(countQuery, params);

        int count = ((Long) countQuery.uniqueResult()).intValue();
        if (searchOption != null)
            return new PagingResult<U>(searchOption.getPage(), count, searchOption.getSize(), list);
        else
            return new PagingResult<U>(0, count, 0, list);
    }


   public static StringBuffer retriveCountQueryFromHql(StringBuffer jql) {
        if(jql.indexOf("order by")>=0)
            jql.replace(jql.indexOf("order by"), jql.length(),"");
        String mainQuery = jql.toString();

        jql = new StringBuffer(jql.toString().replace('\t', ' '));
        int firstIndexPBas = jql.indexOf(")");
        int firstIndexPBaz = jql.lastIndexOf("(", firstIndexPBas);
        while (firstIndexPBas > 0) {
            for (int i = firstIndexPBaz; i < firstIndexPBas + 1; i++)
                jql.replace(i, i + 1, "*");
            firstIndexPBas = jql.indexOf(")");
            firstIndexPBaz = jql.lastIndexOf("(", firstIndexPBas);
        }
        int Indexfrom = jql.indexOf(" from ");
        return new StringBuffer(" " + mainQuery.substring(Indexfrom, jql.length()));
    }

    public void applyDafaultAuthorizeFilter(Session session) {
        Filter filter = session.enableFilter("defaultFilter");
        filter.setParameter("userId", SecurityUtility.getAuthenticatedUserId());
        filter.setParameter("orgId", SecurityUtility.getAuthenticatedUserOrganization().getId());
    }

Query query = getEntityManager().createQuery("select u.lastname,count(*) from Personel u group by u.lastname;");

List<YourEntity> list = query.getResultList();

String hql = "select count(*) from (select u.lastname,count(*) from tbl_personel u group  by u.lastname)";

Query query = session.createQuery(hql);

List listResult = query.list();

select u.lastname, count(u) 
from Personel u 
group by u.lastname

select count(*) 
from (
    select u.lastname, count(*) 
    from tbl_personel u 
    group  by u.lastname
) as tbl_aggr

select u.firstname, u.lastname
from Personel u 
group by u.firstname, u.lastname;

select sum(count(distinct u.lastname))
from Personel u 
group by u.firstname, u.lastname;