Each record in a Key-Sequenced
Data Set (KSDS) has a key that contains a unique value. KSDS records
are retrieved by their key sequences. The key is a contiguous portion
of the record and is defined when the data set is created. A KSDS
is always defined with a prime index that relates the record's key
value to its relative location in the data set. VSAM uses the index
to locate a record for retrieval and to locate a collating position
for record insertion. A KSDS is the most flexible approach for most
applications because the record can be accessed directly via the key
field. Access is not dependent on the physical location of the record
in the data set.
You can read, add, update,
and erase KSDS records in SAS programs. The options that are associated
with each of these operations are described in the following sections.
In many cases, the option's meaning depends on how it is used within
a SAS program. (Loading KSDS records is discussed separately in
Defining and Loading a VSAM Data Set.)
Here are two helpful
tables and their descriptions:
There are examples
of reading, adding, updating, and performing combined operations on
a KSDS data set. The examples are based on the STUDENT data set described
in
Sample STUDENT Data Set. You can run
the examples by using the sample programs provided in the Help system
and following the steps to define and load a KSDS described in
Defining and Loading a VSAM Data Set.