Question

我想知道从2家商店租来的人数。

架构如下。

final Cursor cursor = myDb.cautarevenituri();

    // The desired columns to be bound
    final String[] columns = new String[] {
            DatabaseHelper.COL_2,
            DatabaseHelper.COL_3
    };

    int[] toviewids = new int[] { R.id.nume_item,R.id.valoare_item};
    dataAdapter = new SimpleCursorAdapter(getActivity().getBaseContext(),R.layout.item_layout,cursor,columns,toviewids,0);
    //
    final ListView listView = (ListView)getView().findViewById(R.id.listView_venituri);

    listView.setAdapter(dataAdapter);
    listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view,
                                       int position, long arg3) {
            Toast.makeText(getActivity(), " " + position, Toast.LENGTH_LONG).show();

            //delete from listview in database and listview too??
            //
            //

            return false;
        }

    });

通过此查询，我可以获得从2家商店租借的客户列表。

Rental table
----------------------------------------------------
rental_id   int(11) NO  PRI 
rental_date datetime    NO  MUL 
inventory_id    mediumint(8) unsigned   NO  MUL 
customer_id smallint(5) unsigned    NO  MUL 
return_date datetime    YES     
staff_id    tinyint(3) unsigned NO  MUL 
last_update timestamp   NO      CURRENT_TIMESTAMP


Inventory table
---------------------------------------------------
inventory_id    mediumint(8) unsigned   NO  PRI 
film_id smallint(5) unsigned    NO  MUL 
store_id    tinyint(3) unsigned NO  MUL 
last_update timestamp   NO      CURRENT_TIMESTAMP

如何将计数作为同一sql语句的一部分来查找？

Answer 1

您将使用两个聚合。第一个是从两个商店租来的人。第二个将它们加起来。所以：

select count(*)
from (select r.customer_id
      from rental r join
           inventory i
           on r.inventory_id = i.inventory_id
      group by r.customer_id
      having count(distinct i.store_id) = 2
     ) r;

Answer 2

select count(*) from(
    select customer_id 
    from rental r , inventory i 
    where r.inventory_id = i.inventory_id 
    group by customer_id 
    having count(distinct i.store_id) = 2);

你必须在内部查询中汇总你的结果，所以你必须用另一个计算所有结果的查询来说明查询。

Answer 3

select r.customer_id, count(*) 
from rental r
join inventory i 
on r.inventory_id = i.inventory_id 
where i.store_id = 2
group by r.customer_id

MySql查找一组后的总计数

3 个答案: