| SAS Component Language: Reference |
When an application
opens a SAS table, its TDV is empty. However, to enable the program to work
with the SAS table columns, SCL provides functions for copying table rows
one at a time from the SAS table to the TDV. Once column values for a row
are in the TDV, you can copy these values into the SCL data vector (SDV),
and the application can manipulate the column values.
Before you can display or manipulate the values of SAS
table columns, those columns must be linked to SCL variables through the TDV
and the SDV. Special SCL functions and storage locations facilitate the transfer
of values between SAS table columns and SCL variables. Path of Data in SAS Table "Read" and "Write" Operations illustrates the SDV and TDV
that are created for an application that opens a SAS table. This figure shows
the paths that rows take when they are read from the table, displayed in the
window, processed, and then returned to the table.
Path of Data in SAS Table "Read" and "Write" Operations
![[IMAGE]](./images/01332652.gif)
Two steps are required in order to
transfer data from
an open SAS table to an SCL program:
- The values of the columns in a row in the open
SAS table are copied into the TDV.
- The values of the columns in the TDV are copied
to the SDV, which contains all of the SCL variables (window variables, nonwindow
variables, system variables, and so on). The transfer of data from the TDV
to the SDV can be either automatic (when the SET routine is used) or under
program control (when the GETVARC or GETVARN functions are used).
Once the values are in the SDV, you can manipulate them
by using SCL statements. Two steps are also required in order to transfer
data from an SCL program to an open SAS table:
- The column values in the SDV are transferred to
the TDV. The transfer of data from the SDV to the TDV can be either automatic
(when the SET routine is used) or under program control (when PUTVARC or PUTVARN
is used).
- The values in the TDV are written to the columns
in a row in the open table.
When a SAS table is opened, SAS software determines the control
level for the table. The control level determines the extent to which access
to the table is restricted. For example, an application may be able to gain
exclusive update access to the entire SAS table, or it may be able to gain
exclusive update access to only the row that is currently in use. In either
case, there are ramifications for any users or applications that need to access
the SAS table at the same time. You can open a SAS table with one of the following
control levels:
- RECORD
- provides exclusive update access only to
the SAS table row that is currently in the TDV (as with the FETCH and FETCHOBS
functions). With this control level, the same user can open the same SAS table
multiple times (multiple concurrent access). In addition, if SAS/SHARE software
is used, then multiple users can open the same SAS table simultaneously for
browsing or for editing. For more information, see SAS/SHARE User's Guide.
- MEMBER
- provides exclusive update access to an entire
SAS table. While this control level is in effect, no other user can open the
table, and the same user cannot open the table multiple times.
|
| Specifying a Control Level |
When you use the OPEN function to open a SAS data set in UPDATE
mode, by default the table is opened with RECORD-level control. However,
in SCL you can use the OPEN function with the SAS data set option CNTLLEV=
to set the control level when a SAS table opens. See OPEN for more information.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
