I have a table named friends with following structure:
我有一个名为friends的表，结构如下：
id, from_id, to_id, confirmed, ....
This table contains the list of all friends of all users. The from_id and to_id contain ids of the users where from_id is the one who actually sent the friend request.
此表包含所有用户的所有朋友的列表。 from_id和to_id包含用户的id，其中from_id是实际发送好友请求的用户。
Now, I need to select the list of all the friends of a particular user into.
现在，我需要选择特定用户的所有朋友的列表。
Is is better to do it using the following query or a query with union:
最好使用以下查询或带有union的查询来执行此操作：
"select (from_id + to_id)- $user_id as friend_id, ... from friends where from_id=$user_id or to_id=$user_id"
3 个解决方案
#1
1
Although I love your mathematic-fan solution I think it is not considering overflow issues. For example: what would happen if you add two extremely big numbers?
虽然我喜欢你的数学风扇解决方案，但我认为它并没有考虑溢出问题。例如：如果添加两个非常大的数字会发生什么？
Apart from that, your solution relies on a numeric user_id. Using a union might take a bit more (you should test that to make sure) but will work with any data type.
除此之外，您的解决方案依赖于数字user_id。使用联合可能需要更多（您应该测试以确保）但可以使用任何数据类型。
#2
1
I would use a union (make sure you have indexes on from_id and to_id):
我会使用union（确保你有from_id和to_id的索引）：
select from_id from friends where to_id = $user_id
union
select to_id from friends where from_id = $user_id
It's more clear this way in my opinion.
在我看来，这种方式更清晰。
#3
1
assuming you have keys on the ids the union will certainly be better, then performing the arithmetic operations.
假设你有关于id的键，联合肯定会更好，然后执行算术运算。
#1
1
Although I love your mathematic-fan solution I think it is not considering overflow issues. For example: what would happen if you add two extremely big numbers?
虽然我喜欢你的数学风扇解决方案，但我认为它并没有考虑溢出问题。例如：如果添加两个非常大的数字会发生什么？
Apart from that, your solution relies on a numeric user_id. Using a union might take a bit more (you should test that to make sure) but will work with any data type.
除此之外，您的解决方案依赖于数字user_id。使用联合可能需要更多（您应该测试以确保）但可以使用任何数据类型。
#2
1
I would use a union (make sure you have indexes on from_id and to_id):
我会使用union（确保你有from_id和to_id的索引）：
select from_id from friends where to_id = $user_id
union
select to_id from friends where from_id = $user_id
It's more clear this way in my opinion.
在我看来，这种方式更清晰。
#3
1
assuming you have keys on the ids the union will certainly be better, then performing the arithmetic operations.
假设你有关于id的键，联合肯定会更好，然后执行算术运算。