SAS/ACCESS 9.2 for Relational Databases: Reference, Fourth Edition

Data Integrity and Security 4 Potential Result Set Differences When Processing Null Data 31libname myoralib oracle user=testuser password=testpasspath=’myoraserver’ updatelock_type=row;Note: Each SAS/ACCESS interface supports specific options; see the SAS/ACCESSdocumentation for your DBMS to determine which options it supports. 4Customizing DBMS Connect and Disconnect ExitsTo specify DBMS commands or stored procedures to run immediately after a DBMSconnection or before a DBMS disconnect, use the DBCONINIT= and DBCONTERM=LIBNAME options. Here is an example:libname myoralib oracle user=testuser password=testpasspath=’myoraserver’ dbconinit="EXEC MY_PROCEDURE";proc sql;update myoralib.mytable set acctnum=123where acctnum=567;quit;When the libref is assigned, the SAS/ACCESS engine connects to the DBMS andpasses a command to the DBMS to execute the stored procedure MY_PROCEDURE. Bydefault, a new connection to the DBMS is made for every table that is opened forupdating. Therefore, MY_PROCEDURE is executed a second time after a connection ismade to update the table MYTABLE.To execute a DBMS command or stored procedure only after the first connection in alibrary assignment, you can use the DBLIBINIT= option. Similarly, the DBLIBTERM=option enables you to specify a command to run before the disconnection of only the firstlibrary connection, as in the following example:libname myoralib oracle user=testuser password=testpassdblibinit="EXEC MY_INIT" dblibterm="EXEC MY_TERM";Potential Result Set Differences When Processing Null DataWhen your data contains null values or when internal processing generatesintermediate data sets that contain null values, you might get different result setsdepending on whether the processing is done by SAS or by the DBMS. Although inmany cases this does not present a problem, it is important to understand how thesedifferences occur.Most relational database systems have a special value called null, which means anabsence of information and is analogous to a SAS missing value. SAS/ACCESStranslates SAS missing values to DBMS null values when creating DBMS tables fromwithin SAS. Conversely, SAS/ACCESS translates DBMS null values to SAS missingvalues when reading DBMS data into SAS.There is, however, an important difference in the behavior of DBMS null values andSAS missing values:3 A DBMS null value is interpreted as the absence of data, so you cannot sort aDBMS null value or evaluate it with standard comparison operators.3 A SAS missing value is interpreted as its internal floating-point representationbecause SAS supports 28 missing values (where a period (.) is the most commonmissing value). Because SAS supports multiple missing values, you can sort a SASmissing value and evaluate it with standard comparison operators.