sql计算2个值共享第三个值的次数

Question

我有2个表，我可以加入一个共同的id。但是，一个表有人名，另一个表有公司名。

people table

company table

如何生成查询结果，我可以计算每个人与每个公司共享相同ID的次数？

Answer 1

你的桌子数据看起来很奇怪。但是这里去了

SELECT p.person,COUNT(*) as share_count
FROM people p
INNER JOIN company c
ON c.id = p.id
GROUP BY p.person

结果

person  share_count
dave    3
mark    4
sara    3

http://sqlfiddle.com/#!9/aba04/3

如果您想按p.id和p.person分组

SELECT p.id,p.person,COUNT(*) as share_count
FROM people p
INNER JOIN company c
ON c.id = p.id
GROUP BY p.id,p.person

结果

id  person  share_count
1   dave    1
1   sara    1
2   mark    2
2   sara    2
3   dave    2
3   mark    2

http://sqlfiddle.com/#!9/aba04/5

更新将share_count除以（不同人的COUNT）

SELECT p.person,COUNT(*) as share_count,COUNT(*)/(SELECT COUNT(DISTINCT person) FROM people) as percent
FROM people p
INNER JOIN company c
ON c.id = p.id
GROUP BY p.person