Illustrated MySQL Query execution flow

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1. Query the cache, determine whether the SQL statement exactly match, and then determine whether there is permission, two judgment is false to the parser parsing statements, for the true extraction of data results returned to the user.

2. Parser parsing. Parser first lexical analysis, syntax analysis, check errors such as quotation marks have not closed, and then generate a parse tree.

3. pretreatment. Preprocessing solves the semantics of unresolved parsers, such as checking the existence of tables and columns, whether aliases are incorrect, and generating a new parse tree.

4. Optimizer does a lot of optimization operations.

5. Generate the execution plan.

6. Query execution engine, responsible for scheduling engine to obtain the corresponding data

7. Return the results.

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Illustrated MySQL Query execution flow