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Will MySQL's non clustered indexes be queried back to the table?

2022-02-04 16:52:53 【Alibaba cloud Q & A】

MySQL Does the non clustered index of the must be queried back to the table ？



Take the answer 1：

not always , If all the fields of the query statement hit the index , Then you don't have to query the return table （ ha-ha , That's what overlay indexing is all about ）.

A simple example , Suppose we build an index on the student table , So when it comes to select age from student where age < 20 When it comes to , On the leaf node of the index , Already included age Information , It will not query back to the table again .

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