A join order is a permutation of the order in which the tables referenced in your query are searched.
Example:
If your query is being used to search two tables - Table A and Table B, the possible join orders are:
- A, B
- B, A
The order in which the tables are searched can have a significant effect on the performance of a query. For this reason, the Query Processor calculates the Cost for each Access Plan, and then uses the results to determine which joint order is the most efficient.