Introduction to MySQL index

Xiao Wu 2021-01-23 23:16:57
introduction mysql index


Index introduction

Index is help MySQL Data structure for efficient data acquisition .

The purpose of indexing is to improve query efficiency , Similar to dictionary , It can be understood as “ Arrange order well Of Quick search data structure ”.

Database besides data itself , It also maintains a data structure that satisfies a specific query algorithm , These data structures point to data in some way , In this way, advanced search algorithms can be implemented on the basis of these data institutions , This data structure is the index .

What we usually call index , Generally speaking, it means B+ Trees ( Multiple search trees ) Index of structural organization .

Index structure example

1611377121302.png

Above picture , In order to speed up Col2 Lookup , You can maintain a binary tree as shown in the figure on the right , Each node contains an index key value and a pointer to the physical address of the corresponding data record , In this way, we can quickly get the physical address of the data record through binary search , To find the corresponding data .

The advantages of indexing

Improve the efficiency of data search , Reduce the IO cost .

Improve the efficiency of data sorting , Reduce the CPU Consume .

Disadvantages of indexes

Indexes are actually data tables , Too many indexes take up more disk space .

Index will reduce the speed of addition, deletion and modification , Because every time you operate the data, you need to maintain the index file .

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