Rails Rails 查询数据库，去重求救
表 T
| from | to |
|---|---|
| a | b |
| a | b |
| c | d |
| b | a |
| c | a |
我想要的结果是 查询条件 from = a 或者 to = a 下不重复的数据 并去重 若 from = a，to = xx 或者 from = xx，to = a 只算一条的话 请问如何去重
T.where(from: a).or(T.where(to: a)).select(:from, :to).distinct
补充：因为我要的是 xx 哪个数据 目前对取出的数据通过 array.uniq 去重 但这样效率很低吧
SELECT IF(STRCMP(`from`, "a") = 0, `to`, `from`) AS another
FROM `table` WHERE `table`.`from` = "a" OR `table`.`to` = "a" GROUP BY another;
这样？
查询条件 from = a 下不重复的数据
T.where("from=?", "a").group("to").having("count(*) = 1").pluck("to")
若 from = a，to = xx 或者 from = xx，to = a 只算一条的话
T.where("not exist (select * from T t2 where t2.from = t.to and t2.to = t.from) ").group("from, to").having("count(*) = 1").pluck "from, to"
