Hash returning entire table - SAS

Question

I have a query using a hash in the data step as follows:

if _n_ = 1 then do;
    if 0 then 
        set TableA;
    declare hash A(dataset: "TableA");
    A.definekey ("UniqueKeyA" );
    A.definedata ("DataA" );
    A.definedone();
end;

if _n_ = 1 then do;
    if 0 then 
        set TableB;
    declare hash B(dataset: "TableB");
    B.definekey ("UniqueKeyB" );
    B.definedata ("DataB" );
    B.definedone();
end;

rcA = A.find(key:UniqueKeyA);
rcB = B.find(key:UniqueKeyB);

When I run the query, TableA returns rcA and the data as expected, but the hash for TableB for some reason brings every column from TableB with it. These queries look identical to me and I can't think of anything qualitatively different between the tables that would cause them to act differently, but I don't know much about SAS.

Explicitly, if my original table is

UniqueKeyA      UniqueKeyB
    1                A
    2                B
    3                C

and TableA is

UniqueKeyA    [...Other TableA columns...]   DataA
    1                                          53
    3                    ...                   46

and TableB is

UniqueKeyB    [...Other TableB columns...]   DataB
    B                                         .45
    C                    ...                  .22

my resulting table is

UniqueKeyA      UniqueKeyB   rcA   DataA   rcB   [...Other TableB columns...]   DataB
    1                A        0      53     21
    2                B       513            0                                     .45
    3                C        0      46     0               ...                   .22

This doesn't make sense to me, since the hashes seem very basic, and although theyre identical only one of them returns every column.

Please let me know if you need more information, thanks!

Also, I have another question about these same hashes entering values into the data column even though, for example, rcA doesn't equal 0. That question is here: Hash find method entering values despite returning non-zero - SAS

Answer 1

This line:

if 0 then 
        set TableB;

is where the columns come from. This is a 'lazy' way of avoiding the uninitialized variable message that would appear from the hash creation if there isn't something technically initializing the variables before the hash. It's fine if you are bringing every variable in, but of course if you're only bringing 2 and you have 40, you get 38 extras that you don't much want. They're empty, but still unneeded.

Add (keep=uniquekey datab) to the set TableB statement and it should get rid of those other columns.