ASA SQL User's Guide
Query Optimization and Execution
How the optimizer works
Underlying assumptions
Traditionally, high performance database servers have relied heavily on the presence of a knowledgeable, dedicated, database administrator. This person spent a great deal of time adjusting data storage and performance controls of all kinds to achieve good database performance. These controls often required continuing adjustment as the data in the database changed.
Adaptive Server Anywhere learns and adjusts as the database grows and changes. Each query betters its knowledge of the data distribution in the database. Adaptive Server Anywhere automatically stores and uses this information to optimize future queries.
Every query both contributes to this internal knowledge and benefits from it. Every user can benefit from knowledge that Adaptive Server Anywhere has gained through executing another user's query.
Statistics-gathering mechanisms are thus an integral part of the database server, and require no external mechanism. Should you find an occasion where it would help, you can provide the database server with estimates of data distributions to use during optimization. If you encode these into a trigger or procedure, for example, you then assume responsibility for maintaining these estimates and updating them whenever appropriate.