MongoDB复合索引用法 [英] MongoDB compound index usage

问题描述

假设我有以下两个密钥的文件：

Lets say I have document with the following two keys:

1）key1

2）key2

1) key1
2) key2

如果我在两者上创建复合索引..

If I am creating compound index on both of them..

{'key1':1,'key2':1}

运行时只与key1相关的查询是否使用了上面的索引？或者我还需要为key1创建特定的索引？

When running a query relevant only for key1.. does the index above is used? or I need to create specific index only for key1 also?

谢谢

推荐答案

是。在B树索引中，您可以使用列的前缀。

Yes. In a B-tree index, you can use a prefix of the columns.

因此，您可以在'key1'上使用索引进行查询（但不能有效地使用'key2'，索引中的列顺序很重要。）

So you can use the index for a query on 'key1' (but not as efficiently for 'key2', the column order in the index matters).

这与打印电话簿中的情况相同，后者是[lastName，firstName]的索引。您可以使用它来轻松地通过lastName查找人员（而不是通过firstName轻松查找人员，但仍然比调用所有人并询问他们的名字更有效。）

This is the same situation as in a printed telephone book, which is an index on [lastName, firstName]. You can use that to look up people by lastName easily (and not so easily by firstName, but still more efficient than calling everyone and asking for their first name).

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