Question

我有三个表：域名，注册和跟踪。

我目前有一个所有域名列表和使用此查询的访问者人数：

SELECT sites.id, sites.domain, count(tracking.domain) as tracked FROM sites
LEFT JOIN tracking ON sites.domain = tracking.domain
GROUP BY sites.domain
ORDER BY sites.id;

现在，我还希望从名为signups的新表中获取计数（每个域）。

我已经达到了这个目标：

SELECT sites.id, sites.domain, count(tracking.domain) as tracked, signers.cc FROM sites
LEFT JOIN tracking ON sites.domain = tracking.domain
LEFT JOIN (
SELECT signups.domain, count(*) as cc FROM signups
GROUP BY signups.domain
) as signers
USING (domain)
ORDER BY sites.id;

但这似乎并不完全正确。有什么建议吗？

Answer 1

在这里:(你可以随意添加外部联接，我只是指向正确的方向）

with trackingCount as
(
select sites.domain,
       count(1) as tracked
  from sites,
       tracking
 where tracking.domain = sites.domain
 group by sites.domain),
signupsCount as
(
select sites.domain,
       count(1) as signedUP
  from sites,
       signups
 where signups.domain = sites.domain
 group by sites.domain)
select *
  from trackingCount tc,
       signupsCount sc
 where tc.domain = sc.domain;

给出：

domain  tracked signedUP
A       4       2 
B       1       4

你可以在这里玩弄它：

http://sqlfiddle.com/#!7/bec74/2

如何从两个表中加入三个表

1 个答案: