Using Logical Expressions In SQL

Most of us SAS programmers approach SQL as simply a data extraction and table joining tool. Since most of us have used the data step longer than SQL, we tend to leave the logic programming to the data step with its if/then statements. However, SQL does have a way of assigning values conditionally. With the CASE expression you can test and assign values logically.
The basic syntax is:

CASE value  
   WHEN condition THEN result  
   WHEN condition THEN result  
   ELSE result
END

In the code below I am just assigning a 1 or a 0 to a column/variable named bool_tf.
Using the CASE expression is pretty straightforward and is another great way to use SQL to get more coding done in fewer steps.

data myData;
  input answer $;
datalines;
true
false
true
true
false
false
true
;
proc sql;
  create table a as
  select answer, 
         case substr(answer,1,1)
              when 't' then 1
       when 'f' then 0
  end as bool_tf
  from myData;
quit;