How can the slow execution of a LEFT JOIN query between two tables with approximately 16 million records be addressed?

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There are several ways to address the slow execution of a LEFT JOIN query between two tables with approximately 16 million records:

1. Optimize the database schema and indexing: Ensure that the tables are properly normalized and indexed, as this can improve the speed of queries. Use primary keys, foreign keys, and indexes strategically to speed up the data retrieval process.

2. Use materialized views: If the LEFT JOIN query is used frequently in the application, consider creating a materialized view that stores the results of the query. This can significantly reduce the query execution time as the data is pre-calculated and stored in the view.

3. Implement query caching: Implement caching to store frequently used query results in memory. This can reduce the workload on the database and improve the response time of the application.

4. Use partitioning: If the tables are very large, consider partitioning them into smaller chunks. This can improve query performance as the database can work on a smaller dataset at a time.

5. Optimize the query itself: Analyze the query execution plan and optimize the query by using appropriate join types, filters, and index hints. Make sure that the query is written efficiently and avoid unnecessary operations.

6. Upgrade the hardware: If all other options have been exhausted, consider upgrading the hardware of the database server. This can improve the processing power and speed of the server, which can improve the query execution time.