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

50 Using the DBINDEX=, DBKEY=, and MULTI_DATASRC_OPT= Options 4 Chapter 5reason. If you perform a join and use PROC SQL, you must ensure that the columnsthat are specified through the DBKEY= option match the columns that are specified inthe SAS data set.CAUTION:Before you use the DBINDEX= option, take extreme care to evaluate some characteristicsof the DBMS data. The number of rows in the table, the number of rows returned inthe query, and the distribution of the index values in the table are among the factorsto take into consideration. Some experimentation might be necessary to discover theoptimum settings. 4You can use the DBINDEX= option instead of the DBKEY= option if you know thatthe DBMS table has one or more indexes that use the column(s) on which the join isbeing performed. Use DBINDEX=index-name if you know the name of the index, or useDBINDEX=YES if you do not know the name of the index. Use this option as a data setoption, and not a LIBNAME option, because index lookup can potentially be anexpensive operation.DBINDEX= requires that the join table must have a database index that is definedon the columns involved in the join. If there is no index, then all processing of the jointakes place in SAS, where all rows from each table are read into SAS and SAS performsthe join.Note: The data set options NULLCHAR= and NULLCHARVAL= determine how SASmissing character values are handled during DBINDEX= and DBKEY= processing. 4