How to optimise mysql distinct query?

@jasen 

There are several techniques that can be used to optimize a MySQL DISTINCT query:

1. Use an index: Make sure that you have an appropriate index on the column(s) you are using in the DISTINCT clause. This can greatly improve query performance.
2. Use LIMIT: If you only need a limited number of distinct values, adding a LIMIT clause to your query can significantly improve performance. This will prevent MySQL from having to scan the entire table.
3. Use a derived table: If your DISTINCT query involves multiple tables and complex joins, using a derived table can help improve performance. A derived table is a subquery that is treated as a virtual table, which can be queried more efficiently.
4. Use EXISTS or IN instead of DISTINCT: In certain cases, using EXISTS or IN clauses instead of DISTINCT can improve performance. This is especially true when you are only interested in checking for the existence of a value, rather than retrieving all distinct values.
5. Optimize your database schema: Review your database schema and ensure that it is properly designed for the queries you are executing. This includes normalizing tables, indexing appropriately, and avoiding redundant data.
6. Consider using NoSQL: Depending on the specific requirements of your application, using a NoSQL database instead of MySQL may provide better performance for distinct queries. NoSQL databases are designed to efficiently handle large amounts of data and provide flexible schemas.

It's important to note that the effectiveness of these optimization techniques can vary depending on your specific query and database structure. It is recommended to test and benchmark different approaches to find the most suitable optimization strategy for your needs.