Comparing Outer Unions and Other SAS Techniques

A PROC SQL set operation that uses the OUTER UNION operator is just one SAS technique that you can use to concatenate tables, as shown in the following programs. Program 1 is the PROC SQL set operation that was shown earlier in this chapter. Program 2 uses a different SAS technique to concatenate the hypothetical tables One and Two.

Program 1: PROC SQL OUTER UNION Set Operation with CORR

proc sql;
   create table three as 
      select * from one 
      outer union corr
      select * from two;
quit;

Program 2: DATA Step, SET Statement, and PROC PRINT Step

 data three; 
    set one two; 
 run;
 proc print data=three noobs; 
 run;
These two programs create the same table as output, as shown below.
DATA Step, SET Statement, and PROC PRINT Step
When tables have a same-named column, the PROC SQL outer union does not produce the same output unless the keyword CORR is also used. CORR causes the same-named columns (in this example, the two columns named X) to be overlaid; without CORR, the OUTER UNION operator includes both of the same-named columns in the result set. The DATA step program generates only one column X.
The two concatenation techniques shown above also vary in efficiency. A PROC SQL set operation generally requires more computer resources but might be more convenient and flexible than the DATA step equivalent.
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