Question

我在下面的当前查询将获得所有注册参加活动的评委。该 in子句中的子查询是因为一个事件可以是一天或多天而且评委可以报名参加一个或多个。这很好，但如果它是一个2天的事件和法官注册两者，他们为用户返回2行。我想将它们结合起来，以便显示它们的信息以及两个事件日。我该怎么做呢？

select concat(ej.FirstName, ' ', ej.LastName) as judge, ej.email, ej.phone, ed.EventDate
from EventJudges ej 
inner join EventJudgeXref ejx on ej.Id = ejx.EventJudgeId 
inner join EventDates ed on ejx.EventDateId = ed.Id
where ejx.EventDateId in(SELECT Id FROM EventDates WHERE EventId = 1) 
order by ej.FirstName asc, ej.LastName asc

EventJudgeXref表包含JudgeId和EventDateId供参考。

Answer 1

尝试使用group_concat：

select concat(ej.FirstName, ' ', ej.LastName) as judge,
    ej.email,
    ej.phone,
    group_concat(ed.EventDate) as EventDate
from EventJudges ej 
inner join EventJudgeXref ejx on ej.Id = ejx.EventJudgeId 
inner join EventDates ed on ejx.EventDateId = ed.Id
where ejx.EventDateId in(SELECT Id FROM EventDates WHERE EventId = 1) 
group by ej.Id
order by ej.FirstName asc, ej.LastName asc

SQL Fiddle

更改当前的MySql查询以基于id组合结果

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