mysql - LEFT JOIN 别名的未知列错误

Question

我试图为我的左连接添加别名，以便我可以在同一个表（不同的键）上进行两个连接，但遇到了这个问题。我已将查询剥离到问题所在，以保持简单。

SELECT stock_items.id AS stockid, exchange_rates.rate AS rate
FROM stock_items
LEFT JOIN exchange_rates AS exr ON stock_items.currency = exchange_rates.id

当我运行此查询时，我得到

1054 - 'on 子句'中的未知列'exchange_rates.id'

但是，如果我删除别名，它看起来像这样......

SELECT stock_items.id AS stockid, exchange_rates.rate AS rate 
FROM stock_items 
LEFT JOIN exchange_rates ON stock_items.currency = exchange_rates.id

此查询运行良好...？

Answer 1

如果你添加一个alias，你应该在你的join.

SELECT stock_items.id AS stockid, exr.rate AS rate
FROM stock_items
LEFT JOIN exchange_rates exr ON stock_items.currency = exr.id