将SQL查询限制为每组仅前两个计数 [英] Limit SQL query to only the top two counts per group

问题描述

如果我有一个名为FAVORITE_FLAVOR的数据库表，其中每一行都有用户喜欢的冰淇淋口味.

If I have a DB table called FAVORITE_FLAVOR where each row has a user's favorite flavor of ice cream.

User ID | Flavor      | State
1       | Chocolate   | CA
2       | Vanilla     | ND
3       |   Chocolate | CA
4       | Rocky Road  | CA
5       | vanilla     | CA
6       | Vanilla     | CA
7       | Vanilla     | CA

现在，如果我想查询每个州的两种最受欢迎​​的语言(规范化大小写和空格)，我可以查询:

Now, if I want to query the 2 most popular flavors in each state (normalizing capitalization and whitespace), I could query:

SELECT state, INITCAP(TRIM(flavor)), count(INITCAP(TRIM(flavor))) AS total
FROM favorite_flavor GROUP BY state, INITCAP(TRIM(flavor))
ORDER BY state ASC, total DESC;

哪个返回:

CA | Vanilla    | 3
CA | Chocolate  | 2
CA | Rocky Road | 1
ND | Vanilla    | 1

现在，我只想知道每个州的前2种口味.如何限制查询，以便不再列出Rocky Road.

Now, I only wanted to know the top 2 flavors per state. How do I limit the query so that Rocky Road is no longer listed.

推荐答案

SELECT
   State,
   flv,
   total
FROM (SELECT
         ROW_NUMBER() OVER ( PARTITION BY state ORDER BY count(INITCAP(TRIM(flavor))) DESC ) RowNumber,
         State,
         INITCAP(TRIM(flavor)) flv,
         count(INITCAP(TRIM(flavor))) total
      FROM favorite_flavor
      GROUP BY state, INITCAP(TRIM(flavor))
      ) dt
WHERE RowNumber <= 2
ORDER BY state ASC, total DESC

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