Tune a SQL query, you can follow these general steps:

1. Identify the query’s performance bottleneck(s): Run the query with a profiler or execution plan tool to identify which parts of the query are taking the most time.
2. Optimize the query’s structure: Simplify the query by removing unnecessary joins, subqueries, or expressions. Ensure that the query uses indexes properly and that it is using the most efficient join type.
3. Optimize the query’s data access: Ensure that the query is only accessing the data that it needs. This can be achieved by using appropriate WHERE clauses, and by selecting only the necessary columns.
4. Optimize the query’s execution plan: Experiment with different execution plans by using hints or by restructuring the query. You can also try different parameter settings, such as increasing the buffer pool size or the query cache.

Here are some specific tips that you can use to tune your SQL query:

• Use appropriate indexes: Ensure that the tables being queried have appropriate indexes that match the columns used in the query’s WHERE clause. Indexes can dramatically improve query performance by allowing the database to quickly locate the required data.
• Avoid using subqueries: Subqueries can be performance-intensive, especially if they are nested or if they access large tables. If possible, try to rewrite the query to avoid using subqueries.
• Use the correct join type: Ensure that you are using the correct type of join for your query. For example, INNER JOIN is generally faster than OUTER JOIN, but it only returns rows that have matching values in both tables.
• Avoid using wildcards: Avoid using wildcards such as % in the query’s WHERE clause, as they can force the database to perform a full table scan.
• Limit the number of rows returned: If the query is returning a large number of rows, consider using the LIMIT keyword to limit the number of rows returned.
• Minimize network traffic: If the query is being executed remotely, try to minimize the amount of data that needs to be transferred over the network by selecting only the necessary columns.

Overall, the key to optimizing SQL queries is to understand how the database system works and how to structure queries to take advantage of its strengths. With careful planning and experimentation, you can achieve significant performance improvements in your SQL queries.