所以我有这个查询，完美地工作：

SELECT users.*,
GROUP_CONCAT(categories.category_name) AS categories
FROM users
LEFT OUTER JOIN user_categories ON users.user_id = user_categories.user_id
LEFT OUTER JOIN categories ON user_categories.category_id = categories.category_id
WHERE users.user_city = 'brooklyn'
GROUP BY users.user_id
LIMIT 10;

假设我还有一个包含电话号码的表，对于“用户”来说，用户可以有任意数量的电话号码…我该如何处理与类别完全相同的事情？换句话说，我想获得另一列，其中包含在“电话”表中找到的所有具有相同“
user_id”的phone_numbers，并将它们连接在一起（phone1，phone2，phone3）？我试过了：

SELECT users.*,
GROUP_CONCAT(phones.phone_number) AS phone_numbers,
GROUP_CONCAT(categories.category_name) AS categories
FROM users
LEFT OUTER JOIN phones ON users.user_id = phones.user_id
LEFT OUTER JOIN user_categories ON users.user_id = user_categories.user_id
LEFT OUTER JOIN categories ON user_categories.category_id = categories.category_id
WHERE users.user_city = 'brooklyn'
GROUP BY users.user_id
LIMIT 10;

运气不好…或者至少执行了查询，但是它做了一些奇怪的重复操作…任何帮助都将非常棒！

谢谢！