mysql - 按百分比排序汇总结果？

Question

我的表格“产品”:

id:
1
2
3
4

我的另一个表 'productSet'

id / specification
1  / 1
1  / n
1  / n
1  / n
1  / 1
2  / 1
2  / n
2  / n
3  / 1
3  / n
3  / n
3  / 1
3  / n
3  / n
3  / n
4  / 1
4  / n
4  / n
4  / 1

product.id = productSet.id

count(productSet WHERE id LIKE '1') = 5
count(productSet WHERE id LIKE '1' AND specification LIKE 'n') = 3
percent = (100-((3*100)/5)) = 40%

count(productSet WHERE id LIKE '2') = 3
count(productSet WHERE id LIKE '2' AND specification LIKE 'n') = 2
percent = (100-((2*100)/3)) = 33,33%

count(productSet WHERE id LIKE '3') = 7
count(productSet WHERE id LIKE '3' AND specification LIKE 'n') = 5
percent = (100-((5*100)/7)) = 28,57%

count(productSet WHERE id LIKE '4') = 4
count(productSet WHERE id LIKE '4' AND specification LIKE 'n') = 2
percent = (100-((2*100)/4)) = 50%

我需要结果描述

4 (50%)
1 (40%)
2 (33,33%)
3 (28,57)

请帮我完成这个命令。我不知道从哪里开始。

Answer 1

这是一个简单的聚合查询。好好利用GROUP BY与 SUM()和 COUNT()给你一个准确的答案，而且非常有效。 http://sqlfiddle.com/#!2/95546c/8/0

SELECT id, 
       COUNT(*) AS total_count, 
       SUM(specification <> 'n') AS non_n_count,
       100.0 * SUM(specification <> 'n') / COUNT(*) AS percent
  FROM productSet
 GROUP BY id
 ORDER BY 4 DESC

这里的技巧是实现表达式 specification <> 'n'为表中存在非空值 specification 的每一行生成零值或一值.因此，将这些值相加可以得到满足标准的行数。

ORDER BY 4 DESC按第四列降序排列结果集。