A SAS variable is either CHARACTER or NUMERIC, in type. Normally the SAS CHARACTER type variable is either blank or non-blank, and a SAS NUMERIC type variable is either considered to have a MISSING value or a non-MISSING value.
Since SAS DATE / DATETIME variables are NUMERIC type, you can set a missing value, such as MYDATE=. or if you attempt to use the INPUT function to convert a string to a date and the input-data is invalid, SAS will set the automatic variable _ERROR_=1 which is an indication of a problem - in addition to SAS setting the variable to a missing value, as well.
There is a MISSING function you may find the opportunity to use - check the SAS DOC.
Also, suggest reviewing the DOC on SAS variables.
Scott Barry
SBBWorks, Inc.
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