How to speed up a query when joining two tables: rules and tips?

To speed up a JOIN query between two tables, you can use the following rules and tips:

• Indexes: Ensure that the columns used in the JOIN are indexed. This will significantly speed up the search for matching records.
• Selective column set: Request only the necessary columns to reduce the amount of data transferred.
• Filtering before JOIN: If possible, apply WHERE conditions to the tables before performing the JOIN to reduce the size of intermediate data.
• Use appropriate JOIN type: For example, INNER JOIN is usually faster than OUTER JOIN if it aligns with the logic of the task.
• Statistics and execution plan analysis: Use EXPLAIN (or similar) to analyze the query plan and identify bottlenecks.
• Denormalization: In some cases, data can be pre-joined or materialized views can be used.
• Parallel execution: Some DBMSs allow configuring parallel query execution.

Example of creating indexes to speed up JOIN:

CREATE INDEX idx_rules_key ON rules(key_column);
CREATE INDEX idx_other_key ON other_table(key_column);

After that, JOIN on key_column will execute faster.