1, the client via TCP three-way handshake after establishing connection with mysql server, connect work done by the service side connector, the main processing links, management authority; 2, after the connection is successful, the query will be in the cache lookup record first, if there is the record of the statement, with the data returned to the client; If the cache does not, enter the analyzer, and lexical analysis and syntax analysis of illegal if happen throw an error, the interrupt operation; 3, analyzer analysis after there is no problem, enter the optimizer, query optimization, according to the indexes such as optimal query; 4, after the optimization, into the actuator to execute queries, call the storage engine interface, obtain the query results, finally the query data returned to the client,