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I am learning Hive and wanted to write an optimized HiveQL/SQL query

My table looks like this:

CREATE TABLE sales (dealer VARCHAR(25), make VARCHAR(25), type VARCHAR(25), day INT);
INSERT INTO sales (dealer, make, type, day) VALUES
("Xyz", "Highlander", "SUV", "0"),
("Xyz", "Prius", "HATCH", "1"),
("Xyz", "Prius", "HATCH", "2"),
("Xyz", "Prius", "HATCH", "3"),
("Xyz", "Versa", "HATCH", "1"),
("Xyz", "Versa", "HATCH", "2"),
("Xyz", "Versa", "HATCH", "3"),
("Xyz", "S3", "SEDAN", "1"),
("Xyz", "S3", "SEDAN", "2"),
("Abc", "Forrester", "SUV", "1");

Given a "dealer" D, I want to compute the top N "make" for each "type" in the past X days, in a single query.

SELECT dealer, make, type, COUNT(*) AS frequency FROM sales
WHERE day > 0 AND dealer LIKE 'Xyz' GROUP BY make, type
ORDER BY frequency DESC LIMIT 5

The problem is when using GROUP BY on "make" and "type" for top 1, I will only get:

DEALER, MAKE, TYPE, COUNT
Xyz, Prius, Hatch, 3
Xyz, Versa, Hatch, 3
Xyz, S3, Sedan, 2
...

But I want

Xyz, Prius, Hatch, 3
Xyz, S3, Sedan, 2
...

for EACH "type" the top N.

Could someone help me understand how to write such a query?

SQL Fiddle http://sqlfiddle.com/#!2/df9304/5

****Update****

Seems like rank() would be useful:

Hive getting top n records in group by query

https://blogs.oracle.com/taylor22/entry/hive_0_11_may_15

HiveQL and rank()

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1 回答 1

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在阅读了更多文档和链接问题的提示后：

SELECT dealer, make, rank, type FROM (
    SELECT dealer, make, rank() OVER (PARTITION BY type ORDER BY count DESC) AS rank, type FROM (
        SELECT dealer, make, count(*) AS count, type FROM Sales WHERE dealer = "Xyz" GROUP BY dealer, type, make
    ) CountedSales
) RankedSales
WHERE RankedSales.rank < 3;

内部查询执行计数，中间查询执行 rank()，外部查询限制排名。

销售表内容

hive> select * from Sales;
OK
Xyz      Highlander      SUV    NULL
Xyz      Highlander      SUV    NULL
Xyz      Rouge   SUV    NULL
Xyz      Rouge   SUV    NULL
Xyz      Prius   HATCH  NULL
Xyz      Prius   HATCH  NULL
Xyz      Prius   HATCH  NULL
Xyz      Versa   HATCH  NULL
Xyz      S3      SEDAN  NULL
Xyz      S3      SEDAN  NULL
Xyz      S3      SEDAN  NULL
Xyz      A8      SEDAN  NULL
Xyz      A8      SEDAN  NULL
Xyz      A8      SEDAN  NULL
Xyz      A8      SEDAN  NULL
Time taken: 0.054 seconds, Fetched: 15 row(s)

现在是实际查询。

hive> SELECT dealer, make, rank, type FROM (                                                                          
    >     SELECT dealer, make, rank() OVER (PARTITION BY type ORDER BY count DESC) AS rank, type FROM (
    >         SELECT dealer, make, count(*) AS count, type FROM Sales WHERE dealer = "Xyz" GROUP BY dealer, type, make
    >     ) CountedSales
    > ) RankedSales
    > WHERE RankedSales.rank < 3;
...
Execution completed successfully
MapredLocal task succeeded
OK
Xyz      Prius  1        HATCH
Xyz      Versa  2        HATCH
Xyz      A8     1        SEDAN
Xyz      S3     2        SEDAN
Xyz      Rouge  1        SUV
Xyz      Highlander     1        SUV
Time taken: 28.491 seconds, Fetched: 6 row(s)
于 2014-08-26T02:29:53.893 回答