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What are the common principles in mysql, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

1. Leftmost matching principle

For example, if you build an index (aforce b), there is no need to build an an index, because (aforce b) already contains an an index, so there is no need to create a b index, but the b index still needs to be created separately, because (aforce b) is to satisfy the case of an and b, and only b does not mean.

Of course, an and b should consider the size of these two indexes, and try to choose the small ones as separate indexes. Because it's faster.

First of all, if you can maintain one index less by adjusting the order, then this order often needs to be given priority.

2. According to the principle of equivalence, the fields queried are the same as those in the database, and = match

100% use index.

3. Leftmost prefix matching principle

To use like for fuzzy queries, 1% can use indexes, but 1 cannot.

4. The principle of scope search

If there is a range query in the where statement, only the leftmost index of the federated index can use the range query.

5. The principle of equivalent matching + range matching

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