- Each index is assigned a name and is related to a particular
table based on the ON table-name clause.
- The entries in an index are ordered on a specified column within
the specified table, and arranged in either ascending or descending order.
- The term index key refers to the column (or set of
columns) in a table that is used to determine the order of entries in
an index. Where an index does consist of multiple columns, the most
important column is placed first.
- Further options controlling how and what type of index is created
may be set in the WITH clause; see here.
- A table can have many different indexes associated with its
columns. Each index is created by issuing a separate CREATE INDEX
Many queries to the
EMPLOYEE table reference the employee's
department; therefore, the database designer decides to create an
index using the
DEPT column to improve performance related to these
CREATE INDEX DEPTINDEX
ON EMPLOYEE (DEPT) ;
would direct the creation of an index called
Index name) on the table
EMPLOYEE, using the
DEPT column as indicated in parentheses as the Index key.
The index can be used by the system to provide quick access to
employee data that are subject to conditions related to the employee's
Copyright © Thunderstone Software Last updated: Jun 9 2017