You can't 'directly fetch it from object table' Have a look at the OOTB Query Issue Management which has three joins to different lookups to decode three attributes:
FROM ODF_ISSUE_V2 I
INNER JOIN INV_INVESTMENTS inv ON i.pk_id = inv.id
AND inv.is_active <> 0
INNER JOIN INV_PROJECTS prj ON i.pk_id = prj.prid
LEFT OUTER JOIN SRM_RESOURCES r ON i.assigned_to = r.user_id
LEFT OUTER JOIN PRJ_OBS_ASSOCIATIONS assoc ON inv.id = assoc.record_id
AND @UPPER@(assoc.table_name) = 'SRM_PROJECTS'
LEFT OUTER JOIN PRJ_OBS_UNITS_FLAT flat ON assoc.unit_id = flat.unit_id
LEFT OUTER JOIN CMN_LOOKUPS_V status ON status.lookup_code = i.status_code
AND status.lookup_type = 'RIM_STATUS'
AND status.language_code = @WHERE:PARAM:LANGUAGE@
LEFT OUTER JOIN CMN_LOOKUPS_V category ON category.lookup_code = i.category_type
AND category.lookup_type = 'RIM_CATEGORY_TYPE'
AND category.language_code = @WHERE:PARAM:LANGUAGE@
LEFT OUTER JOIN CMN_LOOKUPS_V priority ON priority.lookup_code = i.priority_code
AND priority.lookup_type = 'RIM_PRIORITY'
AND priority.language_code = @WHERE:PARAM:LANGUAGE@
The bolded section basically the same code, where it uses different lookup_type to determine what Look-up to use. The first lookup is for RIM Status, the second for RIM Category and the third for RIM Priority. The above code could basically be cut-pasted into GEL scripts.
From V15.4 and above, your SQL needs to include the joins to CMN_LOOKUPS_V.
If you are still using V13.3 to V15.3, there are additional views (eg ODF_ISSUE_V) which did the look-up joins for you, but these were dropped in V15.4. So basically ignore this paragraph, as if you are using these versions, then they won't exist in future versions, but, you can review the database code behind these views to give you additional insight on how the look-up joins work.