在LEFT JOIN之后填补缺失值的最佳方法？ [英] Optimal way to fill in missing values after a LEFT JOIN?

问题描述

我将简化我的问题，使核心问题清楚：我有一个查询 TableA INNER JOIN TableB LEFT JOIN TableC 。

I will simplify my problem to make the core issue clear: I have a query that does TableA INNER JOIN TableB LEFT JOIN TableC.

左连接的结果是在结果集中，两列在某些行中可能具有NULL值。为了填写缺失的值，我必须循环查询结果集，并查询另一个数据库，因此首先不能加入
。

The result of the left join is that in the result set, two of the columns might have NULL values in some rows. To fill in the missing values I have to loop over the result set and query another database that has the data (so it is not possible to join in the first place).

我的问题是：当我们需要填写左连接后的结果集的空值时，是否有标准/优化的方法？

My question is: Is there a standard/optimised approach when we need to fill nulls of a result set after a left join?

推荐答案

要填写缺少的值，我必须循环结果集并查询具有数据的另一个数据库（因此首先不可能加入）。

"To fill in the missing values I have to loop over the result set and query another database that has the data (so it is not possible to join in the first place)."

考虑一个不同的解决方案，然后循环填写数据。

Consider a different solution then looping to fill in data.

1.同一服务器上的另一个数据库= =容易只需使用db.schema限定名称加入。

1.Another database on the same server==easy. Just join using db.schema qualified names.

1. 另一台服务器上的另一个数据库，仍然可能取决于您的网络拓扑。然后加入使用server.db.schema限定名称。

1. Another database on a another server, still possibly depending on you network topography. Then join using server.db.schema qualified names.

如果您经常需要，请考虑复制所需的数据。

Consider replicating the data you need if you regularly need to do this.

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