What is mysql execution plan

Mysql execution plan refers to the specific execution strategy and operation sequence adopted by the mysql database management system when executing sql statements. The execution plan is generated by the query optimizer, and it describes the process of MySQL discovering and evaluating SQL queries. It provides important information about how to use indexes, perform join operations, perform sorting, etc. to help developers optimize query performance. The generation process of mysql execution plan involves components such as query parser, query optimizer and executor.

The operating system of this tutorial: Windows 10 system, mysql version 8.0, Dell G3 computer.

MySQL execution plan refers to the specific execution strategy and operation sequence adopted by the MySQL database management system when executing SQL statements. The execution plan is generated by the query optimizer, and it describes the process by which MySQL discovers and evaluates SQL queries. Execution plans provide important information about how to use indexes, perform join operations, perform sorting, and more to help developers optimize query performance.

The generation process of MySQL execution plan involves components such as query parser, query optimizer and executor. When a SQL statement is sent to the MySQL server, it is first parsed by the query parser. Then, the query optimizer generates multiple possible execution plans based on the parsing results, and each execution plan represents an execution strategy. Finally, the query optimizer evaluates the cost of each execution plan through a cost estimator and selects the lowest-cost execution plan as the way MySQL executes SQL.

MySQL's execution plan is generally displayed in a tree structure, and sometimes can also be output in text form. The tree-structured execution plan decomposes the entire query process into multiple operations, such as table scan, index scan, sorting, aggregation, etc. Each operation has its own cost, operation object, and operation preconditions. Developers can determine the performance bottlenecks of SQL statements based on the execution plan, and then optimize accordingly.

Some important information in the execution plan includes:

1. Scan type: For table scan operations, the execution plan will clearly indicate whether it is a full table scan or an index is used scanning. A full table scan usually means lower performance because all rows of the entire table need to be traversed, while an index scan means that MySQL uses an index to speed up the query.

2. Access type: The execution plan will tell the developer how to access the table, including sequential access, unique index access, range access, etc. For example, if unique index access is used, it indicates that a unique index column is used in the query condition, and MySQL can directly locate the required rows through the index, thus improving execution efficiency.

3. Connection type: If the query involves connection operations of multiple tables, the execution plan will display the connection type. Common join types include nested loop joins, hash joins, sort-merge joins, etc. Different connection types have different consumption of system resources and performance, so you can judge whether the connection operation needs to be optimized based on the execution plan.

4. Sorting and aggregation operations: If the query contains sorting and aggregation operations, the execution plan will show the corresponding sorting and aggregation methods. Developers can use this to determine whether these operations need to be optimized, such as whether corresponding indexes need to be created.

By analyzing the execution plan, developers can gain in-depth understanding of how the MySQL database executes SQL statements and the execution cost of each operation. Based on the execution plan, developers can perform targeted optimizations to improve query performance, reduce resource consumption, and improve system response speed. At the same time, the execution plan is also an important tool for developers to debug and optimize SQL statements, which can help locate and solve the problem of slow execution of SQL statements.

In short, the MySQL execution plan is the information generated by the MySQL database management system when executing a SQL statement that describes the query execution strategy and operation sequence. By analyzing execution plans, developers can optimize SQL statements and query performance, improving the efficiency and performance of the database system.

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