Shulou(Shulou.com)06/01 Report--

With regard to the parsing of the COUNT () function in the Mysql database, most programmers and database engineers have a big difference between Count (1) and Count (*). Some say that Count (1) has better query performance than Count (*), and some say it is lower.

Count (1) is usually queried by the primary key ID index, while Count (*) is queried by the index of all fields.

Count () function parses the execution process-through the index comparison, only the primary key index will take the primary key index, if there is a secondary index, the secondary index will be executed, multiple secondary indexes will go, and the field with the least number of bytes will be queried.

There is no fundamental difference between them, but during execution, Count (*) needs to be parsed internally into Count (1) by Mysql.

So don't dwell on this problem, there are all kinds of things on the Internet, here is a brief explanation for you, the above description has been proved by the test!

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