Often, SQL Anywhere can evaluate search conditions with the aid of indexes. Using indexes speeds optimizer access to data
and reduces the amount of information read and processed from base tables. For example, if a query contains a search condition
column-name=value, and an index exists on the column, an index scan can be used to read only those rows of the table that satisfy the search
condition. Indexes also improve performance dramatically when joining tables.
When executing a query, SQL Anywhere chooses how to access each table. 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.
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