# Joins and performance

Joins, SQL statements in which Derby selects data from two or more tables using one or more key columns from each table, can vary widely in performance. Factors that affect the performance of joins are join order, indexes, and join strategy.

- Join order overview
  The Derby optimizer usually makes a good choice about join order. This section discusses the performance implications of join order.
- Join strategies
  The most common join strategy in Derby is called a nested loop. For each qualifying row in the outer table, Derby uses the appropriate access path (index or table) to find the matching rows in the inner table.

Parent topic: Performance and optimization
Related concepts
Index use and access paths
Derby's cost-based optimization