MySQL -- index of InnoDB storage engine

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One 、 file

frm： Table structure file
ibd： Data is index

Q： Why do you mean InnoDB Index is data , Data is index ？
A： stay InnoDB Inside , It uses primary key as index to organize data storage , So the index file and the data file are the same
Pieces of , All in .ibd In the document . stay InnoDB On the leaf node of the primary key index , It stores our data directly .

Q： a sheet InnoDB Your table may have many multiple indexes , There must be only one copy of the data , Which index leaf node is the data on ？
A： There is a clustered index / Cluster index

Two 、 Clustered index / Cluster index / primary key

If a table has both primary key indexes and other indexes ：
primary key ： It's a clustered index , Determine the physical storage order of data rows , Leaf nodes store data
Other indexes ： It's a secondary index / Secondary index , The leaf node stores the value of the primary key

Definition ： The logical order of index key values is consistent with the physical storage order of table data rows .
Example ： The list of dictionaries is sorted by pinyin , The content is also sorted by Pinyin , This kind of directory sorted by pinyin is called clustered index .

3、 ... and 、 Secondary indexes / Secondary index

When I People use name Cable lead check Inquiry One strip remember record , it Meeting stay Two level Cable lead Of leaf Son section spot look for To name=bobo, Get the primary key value id=1, Then go to the leaf node of the primary key index to get the data .

From this perspective , Because the primary key index scans one tree less than the secondary index B+Tree, Its speed will be relatively faster .

Four 、 If there is no primary key or index in the table , Where is the data stored ？

Reference link ：【 Official website 】innodb-index-types

1、 If we define a primary key (PRIMARY KEY), that InnoDB Will choose the primary key as the clustered index .
2、 If the primary key is not explicitly defined , be InnoDB Will choose the first one that does not contain NULL The unique index of the value is used as the primary key index
lead .
3、 If there is no such unique index , be InnoDB Will choose built-in 6 Byte long ROWID As a hidden clustered index ,
It will increase the primary key as the row record is written .