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In a normal query, as shown below, you see an infinite list of users displayed

select * from t_user 
Copy the code

Do you know what happens when you click execute query??

1 Step 1 Establish a connection

In the first step, your client will connect to the database. In this case, the connector is responsible for establishing the connection with the client, obtaining permissions, and maintaining and managing the connection.

The connector then validates the username and password information you provide to create the connection

Step 2 Classic query cache

Once the connection is established, the second step is to query the cache. If the query has been executed, the mysql database will cache the query statement and its result in key-value pairs (key is the query statement, value is the query result). If the query statement has been executed, the mysql database will cache the query statement and its result in key-value pairs (key is the query statement, value is the query result)

It is called the classic query cache because MySQL 8.0 removes the entire function of the query cache. The query cache tends to do more harm than good. The invalidation of the query cache is very frequent, and whenever a table is updated, all the query cache on that table is cleared.

3 Step 3 The parser analyzes the syntax

The parser first does “lexical analysis”, analyzing keywords such as SELECT and update, and then identifying other strings as columns in a table

Then do the syntax analysis, combined with the results of the lexical analysis to check whether the entered SQL statement meets the MySQL syntax

If syntax is not correct, You will receive an error warning “You have an error in your SQL syntax”. General syntax error will indicate the first error position, check the content of “use near”.

Step 4 optimizer

After the parser validates the SQL syntax, MySql knows what the input SQL is going to do. The next step is to perform further optimizations. For example, when the query table has multiple indexes, the optimizer decides which index to use. Or determine the order in which tables are joined when a statement has multiple joins.

5 Step 5 actuator

The executor is used to manipulate the data storage engine, the analyzer analyzes the target of the SQL, the optimizer determines the execution scenario, and the executor performs the responsibility.

The completion of

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