Hql语句注意事项总结(收藏hbcui1984的总结)

1.在Hql中使用group by的问题

(1)使用统计函数作为输出结果
select sum(total),sum(totalup) from AD where aid=? and fid=? and vdatetime>=? and vdatetime<=? group by aid
(2)使用统计函数作为查询约束条件
select uid from MM group by uid having count(*)>? and min(m_date)<?
(3)使用group by 时有关约束条件的问题

如果约束条件是单个字段,则必须用where,并且where要放在group by之前,如:

select cityname from MI where vdatetime>=? and vdatetime<? group by cityname
如果约束条件是统计函数,则要使用having,并且having要放在group by之后,如:(2)

(4)其实,在某些场合,group by可以用distinct代替,如以下两条语句功能相同:

select cityname from MI where vdatetime>=? and vdatetime<? group by cityname
select distinct cityname from MI where  vdatetime>=? and vdatetime<?


2.在count()中使用别名问题


select count(*) from MipMailconfig as MipMailconfig where MipMailconfig.uid <> ? and MipMailconfig.email = ?-- 正确
select count(MipMailconfig.*) from MipMailconfig as MipMailconfig where MipMailconfig.uid <> ? and MipMailconfig.email = ?-- 错误
3.关于Integer和Long的问题

在Hibernate3.2中，所有的计数都要用Long，用Integer的话就会有问题.
        List list=this.find("select count(*) from MMC as MMC where MMC.uid <> ? and MMC.email = ?",new String[]...{uid,email});
        if(list!=null&&!list.isEmpty())...{
            long count=Long.parseLong(list.get(0).toString());
            if(count>0)
                return true;
            else
                return false;
        }



4.关于参数是数组的问题

在实际的工作中，经常遇到这种情况：
(1)要删除一批数据，传过来一个数组，
(2)或者要查询一批数据，查询条件也是传过来一个数组，
这种情况下如何进行处理？
(1)查询数据，查询条件为一个数组，可以有如下两个方法：
<1>直接拼Hql语句
        String[] ids = ...{"1","2","3"};
        String str="";
        for(int i=0;i<ids.length;i++)...{
            str+="'"+ids[i]+"'";
            if(i!=(ids.length-1))
                str+=",";
            }

        List list;
        list = appinfoManager.find("from Appinfo where id in ("+str+")");
        if(list!=null)...{
            for(int i=0;i<list.size();i++)...{
                Appinfo app = (Appinfo)list.get(i);
                System.out.println(app.getAppname());
            }
            }
        System.out.println("共有"+list.size()+"条记录");
<2>利用回调函数处理    public List getApList() ...{
        return (List)this.getHibernateTemplate().execute(new HibernateCallback() ...{

        public Object doInHibernate(Session session) throws HibernateException, SQLException ...{
            String[] ids = ...{"1","2","3"};
            String  hql=  "from Appinfo where id  in  (:ids)";
            Query query = session.createQuery(hql);
            List list = query.setParameterList("ids", ids).list();
            return list;
        }
        });
    }
(2)删除数据，参数为数组，利用回调函数   
public void delInArray() ...{
        this.getHibernateTemplate().execute(new HibernateCallback() ...{

        public Object doInHibernate(Session session) throws HibernateException, SQLException ...{
            String[] ids = ...{"1","2","3"};
            String  hql=  "delete Appinfo where id  in  (:ids)";
            Query query = session.createQuery(hql);
            query.setParameterList("ids", ids).executeUpdate();
            return null;
        }   
        });   
    }