The SQL optimization specifications consist of the following optimization methods:

• SQL optimization specification for a used index
• SQL optimization specification for a join method
• SQL optimization specification for a subquery execution method

The SQL optimization options consist of the following optimization methods:

1. Forced nest-loop-join
2. Making multiple SQL objects
3. Increasing the target floatable servers (back-end servers for fetching data)
4. Prioritized nest-loop-join
5. Increasing the number of floatable server candidates
6. Priority of OR multiple index use
7. Group processing, ORDER BY processing, and DISTINCT set function processing at the local back-end server
8. Suppressing use of AND multiple indexes
9. Rapid grouping processing
10. Limiting the floatable target servers (back-end servers for fetching data)
11. Separating data collecting servers
12. Suppressing index use
13. Forcing use of multiple indexes
14. Suppressing creation of update-SQL work tables
15. Deriving high-speed search conditions
16. Applying a key condition that includes a scalar operation
17. Facility for batch acquisition from functions provided by plug-ins

The SQL extension optimizing options consist of the following optimization methods:

1. Application of optimizing mode 2 based on cost
2. Hash join, subquery hash execution
3. Suppressing foreign server execution of SQL statements that contain join operations
4. Forcing foreign server execution of SQL statements that contain direct products
5. Suppressing derivation of unconditionally created high-speed search conditions for foreign server execution