[英]SQL query to count rows grouped by an ID, but limit count on each group
[英]Select rows grouped by keyword but weight each group instead of using COUNT()
我使用MySQL數據庫服務器,並且有一個名為keywords
的表,其結構如下:
kewyord_name | product_id
以及關鍵字列表。 我可以使用以下查詢根據列表對keywords
表進行排序:
SELECT *, COUNT(*)
FROM keywords
WHERE keyword_name IN (comma separated list of keywords)
GROUP BY product_id
HAVING COUNT(*) > 2
ORDER BY COUNT(*) DESC
有沒有一種方法可以增加關鍵字的權重,即對於某些關鍵字而言,COUNT(*)要增加一個以上?
如果您在關鍵字表中添加“權重”列,則可以使用總和(權重)和具有總和(權重)來代替Count(*)...
編輯:
select productid, Sum(weights.weight)
from Keywords
Join (Select 'keyword1' as keyword, 2 as weight
Union All
Select 'keyword2' , 5
Union All
Select 'keyword3', 6
) as weights
on Keywords.keyword_name = weights.keyword
group by productid
having Sum(weights.weight) > somevalue
order by weights.weight desc
使用COUNT(*)函數,每行只能加1。 如果希望以不同的方式對待關鍵字,則可以將SUM()函數與case塊一起使用。
例如,假設您有關鍵字This
, that
, these
。 如果你想關鍵字this
和that
有重量的3, these
是2的重量,和其他任何權重為1,你可以這樣做:
SELECT keyword_name,
SUM(CASE WHEN keyword_name IN ('this', 'that') THEN 3
WHEN keyword_name IN ('these') THEN 2
ELSE 1 END) AS weight
FROM myTable
GROUP BY keyword_name;
這是一個SQL Fiddle示例。
為了匹配您已有查詢的設計,您只需要添加having和order by子句:
SELECT keyword_name,
SUM(CASE WHEN keyword_name IN ('this', 'that') THEN 3
WHEN keyword_name IN ('these') THEN 2
ELSE 1 END) AS weight
FROM myTable
GROUP BY keyword_name
HAVING weight > 2
ORDER BY weight DESC;
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