Question

我具有以下数据库架构：

商店包含字段：ID，地址，名称

具有以下字段的产品： id，shop_id，类别（枚举：衣服，家具，电子产品）

有没有一种方法可以编写高效的查询来获取有关商店的信息，因此最终查询将生成有关每个商店的摘要。例如：

@NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        final String details = getItem(position);
        ViewHolder viewHolder;
        ViewHolder mainViewHolder = null;
        if(convertView == null){
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(layout, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.dealInfo = convertView.findViewById(R.id.dealinfo);
            viewHolder.accept = convertView.findViewById(R.id.accept);
            viewHolder.accept.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Toast.makeText(getContext(), details, Toast.LENGTH_SHORT).show();
                }
            });

            convertView.setTag(viewHolder);
        }
        {
            mainViewHolder = (ViewHolder) convertView.getTag();
            mainViewHolder.dealInfo.setText(details);
        }

        return convertView;
    }

Answer 1

使用条件聚合：

select name, count(case when category='clothes' then 1 end) as clothes,
count(case when category='furniture' then 1 end) as furniture,
count(case when category='electronics' then 1 end) as electronic
from
(select name,category from shop inner join product 
on shop.id=product.shop_id)a
group by name

Answer 2

尝试使用Pivot表。

Sql Fiddle

枢轴：

PIVOT通过旋转唯一值来旋转表值表达式从表达式的一列到输出的多列，并在剩余的任何位置执行汇总最终输出中所需的列值

取消枢纽：

UNPIVOT通过旋转列执行与PIVOT相反的操作表值表达式转换为列值。

有关Pivot

的更多信息

select *
from
(
  select name, value
  from(
  select name, category
  from test t
  join shop s on s.id = t.shop_id) as s
  unpivot
  (
    value
    for col in (category)
  ) unp
) src
pivot
(
  count(value)
  for value in ([clothes], [furniture], [electronics])
) piv

Answer 3

如果知道所需的列，我将其写为：

def example_delete_topics(a, topics):
    """ delete topics """

    # Call delete_topics to asynchronously delete topics, a future is returned.
    # By default this operation on the broker returns immediately while
    # topics are deleted in the background. But here we give it some time (30s)
    # to propagate in the cluster before returning.
    #
    # Returns a dict of <topic,future>.
    fs = a.delete_topics(topics, operation_timeout=30)

    # Wait for operation to finish.
    for topic, f in fs.items():
        try:
            f.result()  # The result itself is None
            print("Topic {} deleted".format(topic))
        except Exception as e:
            print("Failed to delete topic {}: {}".format(topic, e))

如果您不知道各列，还可以考虑使用select s.name, sum( (p.category = 'clothes')::int ) as clothes, sum( (p.category = 'furniture')::int ) as furniture, sum( (p.category = 'electronic')::int ) as electronic from shop s join product p on s.id = p.shop_id group by s.name;或动态SQL。

SQL：相关模型的合计计数

3 个答案: