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

41CHAPTER5Optimizing Your SQL UsageOverview of Optimizing Your SQL Usage 41Passing Functions to the DBMS Using PROC SQL 42Passing Joins to the DBMS 43Passing the DELETE Statement to Empty a Table 45When Passing Joins to the DBMS Will Fail 45Passing DISTINCT and UNION Processing to the DBMS 46Optimizing the Passing of WHERE Clauses to the DBMS 47General Guidelines for WHERE Clauses 47Passing Functions to the DBMS Using WHERE Clauses 47Using the DBINDEX=, DBKEY=, and MULTI_DATASRC_OPT= Options 48Overview of Optimizing Your SQL UsageSAS/ACCESS takes advantage of DBMS capabilities by passing certain SQLoperations to the DBMS whenever possible. This can reduce data movement, which canimprove performance. The performance impact can be significant when you access largeDBMS tables and the SQL that is passed to the DBMS subsets the table to reduce theamount of rows. SAS/ACCESS sends operations to the DBMS for processing in thefollowing situations:3 When you use the SQL pass-through facility, you submit DBMS-specific SQLstatements that are sent directly to the DBMS for execution. For example, whenyou submit Transact-SQL statements to be passed to a Sybase database.3 When SAS/ACCESS can translate the operations into the SQL of the DBMS.When you use the SAS/ACCESS LIBNAME statement and PROC SQL, yousubmit SAS statements that SAS/ACCESS can often translate into the SQL of theDBMS and then pass to the DBMS for processing.By using the automatic translation abilities, you can often achieve the performancebenefits of the SQL pass-through facility without needing to write DBMS-specific SQLcode. The following sections describe the SAS SQL operations that SAS/ACCESS canpass to the DBMS for processing. See “Optimizing the Passing of WHERE Clauses tothe DBMS” on page 47 for information about passing WHERE clauses to the DBMS.