With SAS 9, SAS Institute have introduced the sort sort of integrity constraints that have been bread and butter for relational database SQL programs but some SAS programmers may find them more restrictive than they might like. The main one that comes to my mind is the following:
proc sql noprint;
create table a as select a.*,b.var from a left join b on a.index=b.index;
Before SAS 9, that worked merrily with nary a comment but you now will see a warning like this:
WARNING: This CREATE TABLE statement recursively references the target table. A consequence of this is a possible data integrity problem.
In data step, the following still runs without a complaint:
merge a b(keep=index var);
On the surface of it this does look inconsistent. From a database programmer’s point of view having to use different source and target datasets is no hardship but seems a little surplus to requirements for a SAS programmer trained to keep down the number of temporary datasets in an effort to reduce I/O and keep things tidy, an academic concept perhaps in these days of high processing power and large disks. Adding UNDO_POLICY=NONE to the PROC SQL line does make everything consistent again but I see this as being anathema to a database programming type. I do admit to indulging in the override for personal quick and dirty purposes but abiding by the constraint is how I do things for formal purposes like inclusion in an application.