The following query may run slowly (depending on the number and size of the files in the directory) because the directory access server must read the contents of all files in the directory to find the one(s) that match the predicate:

SELECT contents FROM DirAccessProxyTable WHERE filename LIKE 'something%'; 

The following query returns the contents of the single file without causing a directory scan:

SELECT contents FROM DirAccessProxyTable WHERE filename = 'something';

The following query may also run slowly (depending on the number and size of the files in the directory) because the directory access server must do a table scan due to the presence of the disjunct (OR):

SELECT contents FROM DirAccessProxyTable WHERE filename = 'something' OR SIZE = 10;

As an alternative to putting the filename as a literal constant in the query, you can put the file name value into a variable and use the variable in the query:

DECLARE @filename LONG VARCHAR;
SET @filename = 'something';
SELECT contents FROM DirAccessProxyTable WHERE filename = @filename;