MySQL多连接选择结果作为单行中的列

Question

我昨天一直在努力处理这个查询。 我将联接简化到最低限度，因为它产生了非常奇怪的结果。

现在它正在执行我“期望”的操作，但不执行我想要的操作...理想情况下，如果它们是event_attendee_days中的行，则我希望返回一行day_1，day_2和day_3。

SELECT event_attendees.id, event_attendees.name, event_account.name AS company,

case event_attendee_days.days_id
when '1' then "25th"
ELSE "-"
end AS day_1,

case event_attendee_days.days_id
when '2' then "26th"
ELSE "-"
end AS day_2,

case event_attendee_days.days_id
when '3' then "27th"
ELSE "-"
end AS day_3,

event_account.email, event_account.telephone, acct_type, acct, address1, address2,     address3, address4, postcode, business_type, business_desc, signup

FROM event_attendees
JOIN event_account ON event_attendees.acct_id = event_account.id
LEFT JOIN event_attendee_days ON event_attendees.id = event_attendee_days.user_id

WHERE event_attendees.id = "1019"

ORDER BY event_attendees.acct_id

当前产生（在此示例中，我跳过了不需要的文件。）

id   |   day_1  |   day_2  |   day_3
1019 |   25th   |   -      |   -
1019 |   -      |   26th   |   -
1019 |   -      |   -      |   27th

但是我想要

id   |   day_1  |   day_2  |   day_3  | ...
1019 |   25th   |   26th   |   27th   | ...
1020 |   -      |   -      |   27th   | ...

等等。我有一些不同的看法，这是我到目前为止最接近的。 只需将结果压缩为一行，而不会丢失信息:-)

谢谢

Answer 1

试试看：

SELECT
    id,
    MAX(day_1) AS day_1,
    MAX(day_2) AS day_2,
    MAX(day_3) AS day_3
FROM
    event
GROUP BY
    id;

我在这里做了一个SQL Fiddle，请随时在这里进行测试

不过，您仍然需要手动输入所有日期。

希望能帮助到你

PS：在我的小提琴上，该表被命名为“事件”