Question

我想从表格中提取某些东西的最大值（数量（*））。

有效地，我正在努力做的是拉出一个客户最喜欢的品牌。所以他们每年要买300条肥皂，但我想知道他们最喜欢的是哪种。所以max（count（brand_id）基本上就是。

我想这样做：

    SELECT
 transaction.customer_id,
 max(occ) 
 FROM
 (  SELECT 
    transaction.customer_id,
    count(transaction.brand_id) as occ,
    FROM
    transaction

    GROUP BY
    transaction.customer_id,

) AS foo
GROUP BY
transaction.customer_id

提前致谢

Answer 1

你可以这样做：

with cte as (
    select customer_id, brand_id, count(*) as cnt
    from test1
    group by customer_id, brand_id
)
select distinct on (customer_id)
    customer_id, brand_id, cnt
from cte
order by customer_id, cnt desc

请记住，如果有多个品牌对某些客户具有相同的数量，那么您最终会得到一条任意记录。如果要获取所有记录，请使用dense_rank（）函数：

with cte1 as (
    select customer_id, brand_id, count(*) as cnt
    from test1
    group by customer_id, brand_id
), cte2 as (
    select
        customer_id, brand_id,
        dense_rank() over(partition by customer_id order by cnt desc) as rn
    from cte1
)
select customer_id, brand_id
from cte2
where rn = 1

<强> sql fiddle demo

对于PostgreSQL 8.3：

select distinct on (customer_id)
    customer_id, brand_id, cnt
from (
    select customer_id, brand_id, count(*) as cnt
    from test1
    group by customer_id, brand_id  
) as c
order by customer_id, cnt desc;

<强> sql fiddle demo

Answer 2

或like this

 with cte as (
    SELECT 
        transaction.customer_id,
        count(transaction.brand_id) as occ,
        FROM
        transaction

        GROUP BY
        transaction.customer_id
    )

    select max(occ) from cte

最大计数 - PostgreSQL

2 个答案: