Hql语句注意事项总结

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;


}


});


}

http://blog.csdn.net/hbcui1984/archive/2006/12/05/1431011.aspx