mysql - 为什么 left outer join 对我来说失败了？

Question

我看不出有什么问题，但为什么会这样

/* SQL Error (1064): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'left outer join votes on items.id = votes.parent and votes.userid = 1 group by i' at line 2 */


select maxVotes, sum(case when coalesce(votes.id, 0) then 1 else 0 end) votesCast from items where type = 'marker'
left outer join votes on items.id = votes.parent and votes.userid = 1 group by items.id;

我正在使用 mySql 执行此操作。

Answer 1

更改为

select maxVotes, 
       sum(case when coalesce(votes.id, 0) then 1 else 0 end) votesCast 
  from items left outer join votes -- <-- your JOIN clause should go here
    on items.id = votes.parent 
   and votes.userid = 1 
 where type = 'marker' -- <-- and WHERE here
group by items.id;

旁注:即使 MySql 允许在 SELECT 中指定一个不属于 GROUP BY 的字段(在您的情况下为 maxVotes)，但它不是好事要做。您需要对该字段应用聚合函数(MAX、MIN...)。当您执行 GROUP BY items.id 时，无法判断要获取 maxVotes 的哪个值。