MySQL左外连接麻烦 - | 这是一个按小时将交易按价格点分组的查询： SELECT hour(Stamp) AS hour, PointID AS pricepoint, count(1) AS counter FROM Transactions GROUP BY 1,2; ...

左外连接的最大条件。 - | ---------- samples ---------- SamplesID stylenumber stylename status ----------- samples_details ----------- Samples_Details...