SQL query performance has a direct impact on application performance. Slow queries affect not only the database server but also the user experience. Query optimization is therefore an important skill for developers.

The first step is to avoid retrieving unnecessary data. Instead of using SELECT *, select only the columns required by the application. This reduces network traffic and memory usage.

Proper indexing is another key factor. Columns used in WHERE and JOIN conditions can often benefit from indexes. However, too many indexes can slow down write operations, so decisions should be based on execution plans.

Filtering logic, functions applied to columns, pagination strategy and join structure all affect performance. Optimization is not a single setting; it requires looking at queries, table design, indexes and data distribution together.