Postgres慢查询加入第一条记录

Question

我有这个问题：

.swift

我尝试做的是通过加入与交易日期{{匹配的第一个时间记录 SELECT mt.market_coin_id AS coin_id, mt.quantity AS quantity, (ha.price_eur * mt.quantity) as test FROM market_transactions mt JOIN historical_data ha ON ha.id = (SELECT id FROM historical_data WHERE historical_data.coin_id = mt.market_coin_id ORDER BY mt.trade_at <-> snapshot_on LIMIT 1) WHERE mt.user_id = 1 的历史定价表，即时计算价格（test） 1}}

然而查询似乎很慢。

假设所有内容都被编入索引，是否有正确的方法使这个查询更快一点？

historical_data.snapshot_on

mt.trade_at

historical_data

ID    | COIN_ID | SNAPSHOT_ON | PRICE_USD | PRICE_EUR | 
------|---------|-------------|-----------|-----------|
42794 | 422     | 2017-07-31  | 0.0001353 | 0.0001152 | 
42795 | 422     | 2017-08-01  | 0.0001144 | 0.0000968 | 

Answer 1

我会选择这样的事情：

SELECT mt.market_coin_id AS coin_id, mt.quantity AS quantity,
       (SELECT ha.price_eur * mt.quantity
        FROM historical_data ha
        WHERE ha.coin_id = mt.market_coin_id AND
              ha.snapshot_on <= mt.trade_at
        ORDER BY ha.snapshot_on DESC
        LIMIT 1
       ) as test
FROM market_transactions mt
WHERE mt.user_id = 1;

然后您需要market_transactions(user_id, market_coin_id, quantity)和historical_data(coin_id, snapshot_on)上的索引。