| LIBNAME Statement: PC Files on Microsoft Windows |
Controls the format of the WHERE clause when you use the DBKEY
data set option.
| Valid in: |
DATA and PROC steps (when accessing PC files
data using SAS/ACCESS software)
|
| Default value: |
LIBNAME setting
|
If there might be NULL values in the transaction
table or the master table for the columns that you specify in the DBKEY option, then use DBNULLKEYS=YES. When you specify
DBNULLKEYS=YES, and specify
a column that is not defined as DBKEY= NOT NULL, SAS generates a WHERE clause
that finds NULL values. For example, if you specify DBKEY=COLUMN and COLUMN
is not defined as NOT NULL, SAS generates a WHERE clause with this syntax:
WHERE ((COLUMN = ?) OR ((COLUMN IS NULL) AND (? IS NULL)))
This syntax enables SAS to prepare the statement once and use it for
any value (NULL or NOT NULL) in the column. Note that this syntax has the
potential to be much less efficient than the shorter form of the WHERE clause
(presented below). When you specify DBNULLKEYS=NO or specify a column that
is defined as NOT NULL in the DBKEY option, SAS generates a simple WHERE clause.
If there are no NULL values in the transaction table
or the master table for the columns listed in the DBKEY option, use DBNULLKEYS=NO.
If you specify DBNULLKEYS=NO and DBKEY=COLUMN, SAS generates a shorter form
of the WHERE clause. This WHERE clause is generated even if the column that
DBKEY specifies is defined as NOT NULL.
WHERE (COLUMN = ?)
To assign this option to a group of tables, use the
DBNULLKEYS option specified in LIBNAME Options.
Copyright © 2009 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
