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Beginning in Release 8.1 TSLEVEL 1M0, a WHERE statement or data set
option which is optimized with an index may return too few observations.
For the problem to occur, the following conditions must all be true:

  1) the data set must be sorted by a method that sets the sort
     information to VALIDATED=YES,

  2) the data set must have an index created on some variable other
     than the major sort key (for a composite index, the first
     variable in the list must be different than the major sort key),
     and,

  3) the WHERE clause must contain an OR or IN operator which tests
     values for the major sort key.

The following example illustrates the problem:

  DATA A;
    DO I=1 TO 10;
      DO J=1 TO 10;
        OUTPUT;
      END;
    END;
  RUN;
  PROC SORT DATA=A OUT=B (INDEX=(I));
    BY J;
  RUN;
  DATA _NULL_;
    SET B;
    WHERE J IN (2,3) AND I>0;
  RUN;

The second DATA step incorrectly returns only 2 observations.

To prevent the problem, sites should specify the following option in a
system CONFIG file:

  debug= "yoew_opt=1";

This problem is corrected in SAS 9.

A Technical Support hot fix for Release 8.2 TSLEVEL TS2M0 for this
issue is available at:

http://www.sas.com/techsup/download/hotfix/82_sbcs_prod_list.html#004316

For customers running SAS with Asian Language Support (DBCS), this
hot fix should be downloaded from:

http://www.sas.com/techsup/download/hotfix/82_dbcs_prod_list.html#004316

Operating System and Release Information

A fix for Release 8.2 (TS2M0) for this issue is available at:

A fix for Release 8.2 (TS2M0) with Asian Language Support (DBCS) for this issue is available at: