What does analyze in mysql do?

The MySQL ANALYZE command updates table statistics to optimize query performance, including statistics updates, query optimizer improvements, and space release. It works by scanning table data to calculate the number of rows, the number of DISTINCT values, and the distribution of values ​​to generate a more optimized query plan. Perform ANALYZE on frequently queried tables regularly and analyze only key columns for best practices.

The ANALYZE command in MySQL

The ANALYZE command in MySQL is used to collect and update table statistics. Thereby optimizing query performance.

Function

• Statistical update: ANALYZE updates the statistical information of the data in the table, such as the number of rows and the DISTINCT value of each column numbers and the distribution of different values ​​in a column.
• Query optimizer improvements: Based on updated statistical information, the query optimizer can generate more optimized query plans, thereby improving query performance.
• Space release: If there are redundant or outdated statistical information in the table, ANALYZE can release the space and optimize the storage space of the table.

Usage

<code>ANALYZE TABLE table_name;</code>

How it works

The ANALYZE command collects statistical information by scanning part of the data in the table . It performs the following operations for the specified columns in each table:

• Calculate the number of rows
• Calculate the number of DISTINCT values
• Calculate the frequency distribution of each value

By default, ANALYZE scans approximately 20% of the data in the table. The scan range can be configured using the ANALYZE_SAMPLE_SIZE system variable.

Best Practices

• Periodically perform ANALYZE on frequently queried tables to ensure statistics are up to date.
• After making substantial changes to the table (such as inserting or deleting large amounts of data), execute ANALYZE to update statistics.
• If there are many columns in the table, you can analyze only those columns that are frequently used for filtering or joining.

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