Though assuming it's through a DM package, something like this should work:
*SELECT(%PARENT%,PARENTH1,GL_ACCOUNT.%GL_ACCOUNT_SELECT%)
*XDIM_MEMBERSET GL_ACCOUNT = <all>
*WHEN GL_ACCOUNT,PARENTH1
*IS %PARENT%
*REC(FACTOR=1, GL_ACCOUNT = GL_ACCOUNT_SELECT%)
*ENDWHEN
*COMMIT
Normally, if your script is validating but you're not getting any results it's because you haven't passed in enough records. This is resolved through the inclusion of *XDIM_MEMBERSET GL_ACCOUNT = <all>.