ASA SQL User's Guide
Working with Database Objects
Working with indexes
Indexes require extra space and may slightly reduce the performance of statements that modify the data in the table, such as INSERT, UPDATE, and DELETE statements. However, they can improve search performance dramatically and are highly recommended whenever you search data frequently.
For more information about performance, see Using indexes.
Adaptive Server Anywhere automatically indexes primary key and foreign key columns. Thus, manually creating an index on a key column is not necessary and generally not recommended. If a column is only part of a key, an index may help.
Adaptive Server Anywhere automatically uses indexes to improve the performance of any database statement whenever it can. There is no need to explicitly refer to indexes once they are created. Also, the index is updated automatically when rows are deleted, updated or inserted.
For information on altering database object properties, see Setting properties for database objects.