使用计数加入/合并 3 个表

Question

我有 3 张桌子：

人：

pid    name
1      Cal
2      Example
3      Another
4      Person

谈话要点：

tid    pid    talkingPoint
1      1      "..."
2      1      "..."
3      2      "..."

事实：

fid    pid    fact
1      3      "..."
2      2      "..."

我正在尝试将 talkPoints 和事实的计数与“人”结合起来，例如：

pid    name     talkingPoints  facts
1      Cal      2              null
2      Example  1              1
3      Another  null           1
4      Person   null           null

（按talkPoints desc 排序，然后按字母顺序，包括没有任何计数值的“人”行）

我设法将“人”与另一张桌子结合起来：

SELECT a.pid,a.name,
count(b.tid)  
FROM people a, talkingPoints b  
WHERE a.pid=b.pid  
GROUP BY b.pid;

但该查询会忽略计数为零的行（例如“Person”行）

我破解了这个对“talkingPoints”正常工作的查询，但我无法像上面的示例表一样对其进行调整以结合“事实”。

select people.pid, people.name, x.talkingPoints from people left join 
(select pid, name, count(name) talkingPoints from 
(select people.pid, people.name from people
join talkingPoints on talkingPoints.pid = people.pid)
 as talkingPoints group by talkingPoints.pid)
 as x on x.pid = people.pid order by talkingPoints desc, people.name asc;

（可能是一种糟糕的方式，但同时也奏效了）

我如何调整我的查询，以便它们输出一个像我的示例一样的表？

Answer 1

SELECT  a.pid,
        a.name,
        COUNT(DISTINCT b.tid) talkingpoints,
        COUNT(DISTINCT c.fid) facts
FROM    people a
        LEFT JOIN talkingPoints b
            ON a.pid = b.pid
        LEFT JOIN facts c
            ON a.pid = c.pid
GROUP   BY a.pid, a.name
ORDER   BY a.pid

• SQLFiddle Demo

Answer 2

在 SELECT 子句中使用独立的相关子查询，避免了连接造成的重复：

SELECT pid,
       name,
       (SELECT COUNT(*)
        FROM talkingPoints
        WHERE pid = people.pid) AS talkingPoints,
       (SELECT COUNT(*)
        FROM facts
        WHERE pid = people.pid) AS facts
FROM people

SQLFiddle