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The main content of this article is to explain "what is the situation of index failure caused by mysql". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "what is the situation of index failure caused by mysql"?

1. Calculate the usage function or operation of the index column in the query condition.

If an established index field performs a function operation while in use, the index cannot be used.

Because the B+ tree maintained by MySQL for the index is based on the raw data of the field, if you add a function during use, MySQL will not consider the field to be the original field, so it will certainly not be used.

SELECT * FROM student WHERE round (age) = 2

2. Start with% under the like condition.

Select * from student where name like'% bc%'

3. Leftmost matching principle.

The leftmost matching principle means that in a federated index, if the leftmost index in the federated index is used in your sql sentence, the sql sentence can be matched by the federated index when a range query is encountered (>

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