如何编写此查询以显示包含其他字段的计数

为了避免重复来自的所有列,您需要一个子查询。 Person 在您的group by子句中。

SELECT
  p.PersonId,
  p.FirstName,
  p.LastName,
  p.Age,
  coalesce(ph.PhotoCount, 0) as Photocount
FROM
  Person p
  LEFT OUTER JOIN 
     (SELECT PersonId, 
      COUNT(PhotoId) as PhotoCount 
      FROM Photo 
      GROUP BY PersonId) ph
  ON p.PersonId = ph.PersonId 

    SELECT 
       p.PersonId, 
       p.FirstName, 
       p.LastName, 
       p.Age,
       CASE WHEN 
            t.ThePhotoCount IS NULL THEN 0 ELSE t.ThePhotoCount END AS TheCount
       --the above line could also use COALESCE
   FROM 
       Person p 
   LEFT JOIN
         (SELECT 
             PersonId,
             COUNT(*)  As ThePhotoCount
         FROM 
             Photo 
         GROUP BY PersonId) t
    ON t.PersonId = p.PersonID

SELECT P.PersonId, FirstName, LastName,Age, COUNT(PhotoId) AS Num
FROM Person P 
     LEFT OUTER JOIN PHOTO PH ON P.PersonId =  PH.PersonId
GROUP BY P.PersonId, FirstName, LastName,Age

select Person.*, count(PhotoId) from Person left join Photo on Person.PersonId = Photo.PersonId

imo group by应该是解决方案,类似这样的方法对我也适用,即使使用其他表联接:

SELECT meetings.id, meetings.location, meetings.date, COUNT( users.id ) AS attendees
FROM  `meetings`
LEFT JOIN users ON meetings.id = users.meeting_id
WHERE meetings.moderator_id =  'XXX'
GROUP BY meetings.id