When executing a query, SQL Anywhere chooses how to access each table. Indexes greatly speed up the access. When the database server cannot find a suitable index, it resorts to scanning the table sequentially—a process that can take a long time.
For example, suppose you need to search a large database for employees, and you only know their first or last name, but not both. If no index exists, SQL Anywhere scans the entire table. If, however, you created two indexes (one that contains the last names first, and a second that contains the first names first), SQL Anywhere scans the indexes first, and can generally return the information to you faster.
Proper selection of indexes can make a large performance difference. Creating and managing indexes is described in Working with indexes.
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