The difference between MyISAM and InnoDB in MySQL [detailed explanation]

This article mainly introduces the difference between MyISAM and InnoDB in MySQL. I hope it will be helpful to friends in need!

The difference between MyISAM and InnoDB:

1. MySQL uses MyISAM by default.

2.MyISAM does not support transactions, but InnoDB does. InnoDB's AUTOCOMMIT is turned on by default, that is, each SQL statement will be encapsulated into a transaction by default and automatically submitted. This will affect the speed, so it is best to display multiple SQL statements between begin and commit to form a transaction. Go submit.

3.InnoDB supports data row locking, while MyISAM does not support row locking and only supports locking the entire table. Right now The read lock and write lock on the same MyISAM table are mutually exclusive. When MyISAM concurrently reads and writes, if there are both read requests and write requests in the waiting queue, the default write request has a higher priority, even if the read request arrives first, so MyISAM is not suitable for situations where a large number of queries and modifications coexist, as the query process will be blocked for a long time. Because MyISAM is a lock table, a time-consuming read operation will starve other writing processes.

4.InnoDB supports foreign keys, but MyISAM does not.

5.InnoDB has a larger primary key range, up to 2 times that of MyISAM.

6.InnoDB does not support full-text indexing, but MyISAM does. Full-text index refers to char, Create an inverse sorted index for each word in varchar and text (except stop words). MyISAM's full-text index is actually useless because it does not support Chinese word segmentation. The user must add spaces after word segmentation. The grid is then written to the data table, and words with less than 4 Chinese characters will be ignored like stop words.

7.MyISAM supports GIS data, but InnoDB does not. That is, MyISAM supports the following spatial data objects: Point, Line, Polygon, Surface, etc.

8. Count(*) without where uses MyISAM much faster than InnoDB. because There is a counter built into MyISAM. When count(*), it reads directly from the counter, while InnoDB must scan the entire table. Therefore, when executing count(*) on InnoDB, it is generally It must be accompanied by where, and where must contain index columns other than the primary key. Why is there a special emphasis on "other than the primary key" here? Because the primary index in InnoDB is the same as raw The data is stored together, while the secondary index is stored separately, and then there is a pointer pointing to the primary key. Therefore, if it is just count(*), it is faster to use the secondary index to scan, while the primary key mainly returns raw while scanning the index. The effect is greater when using data.

For more MySQL knowledge, you can refer to MySQL Video Tutorial or MySQL Manual!

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