| SAS Component Language: Reference |
When you develop
an application that creates a SAS table, you may want to give users the option
of creating an index for the table. An index, which provides fast access to
rows, is an auxiliary data structure that specifies the location of rows,
based on the values of one or more columns, known as key columns. Both compressed
and uncompressed SAS tables can be indexed by one or more columns to aid in
the subsetting, grouping, or joining of rows. SAS table indexes are particularly
useful for optimizing WHERE clause processing.
SCL provides a set of functions for creating and manipulating
SAS table indexes. However, SCL functions are just one way of building and
querying SAS table indexes. Other ways include:
- the DATASETS procedure in base SAS software
- the INDEX= option
(when you are creating a SAS
table)
- the SQL procedure in base SAS software.
There are two types of indexes: simple indexes and
composite
indexes. A simple index is an index on a single column, and a composite index
is an index on more than one column. A SAS table can have multiple simple
indexes, multiple composite indexes, or a combination of simple and composite
indexes.
SCL provides the following functions for manipulating
indexes:
- ICREATE
- creates an index for SAS tables that are
open in UTILITY mode.
- IVARLIST
- returns a list of one or more columns that
have been indexed for the specified key in the table.
- ISINDEX
- returns the type of index for a column in
a SAS table, as follows:
| BOTH |
The column is a member of both simple
and composite indexes. |
| COMP |
The column is a member of a composite
index. |
| REG |
The column is a member of a regular
(simple) index. |
| (blank) |
No index has been created for the
specified column. |
- IOPTION
- returns a character string that consists
of the options for the specified key and index columns. The options are separated
by blanks.
- IDELETE
- deletes an index for a SAS table that is
open in UTILITY mode. You can delete an index when a program finishes with
it, or if you find that the index is not operating efficiently. Keep in mind
that indexes are not always advantageous. Sometimes the costs outweigh the
savings. For a detailed discussion of when to use indexes, see the information
about SAS files in SAS Language Reference: Concepts.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
