SQL Execution Process

When MySQL executes a SQL statement, it goes through the following steps:

1. Syntax Analysis: MySQL parses the SQL statement to check for syntax correctness. If a syntax error occurs, MySQL returns an error message and stops execution.
2. Lexical Analysis: MySQL breaks down the SQL statement into multiple tokens, such as table names, field names, operators, etc.
3. Semantic Analysis: MySQL performs semantic analysis on the SQL statement to verify the correctness of table names, field names, function names, etc., and also checks whether the current user has permission to execute the operation.
4. Query Optimization: MySQL optimizes the SQL statement by selecting the most efficient query method to achieve the fastest query speed. Based on factors such as table size, indexing status, and data distribution, MySQL chooses an appropriate query method, such as using indexes or temporary tables.
5. Execute Query: MySQL executes the optimized query statement to retrieve the query results. Based on factors such as table size and data distribution, MySQL selects the optimal query method, such as performing a full table scan or using indexes.
6. Return Results: MySQL returns the query results to the client, which receives them via the network protocol. If the query result is too large, MySQL may need to split the data into multiple packets for transmission.