How can I query max date? (PostgreSQL) - sql

Question

Using PostgreSQL, I would like to be able to only see Document IDs with the latest modification time stamp. I am having difficulty getting this working and was wondering if anyone had any pointers?
Here is my current code:
SELECT cmsdw_document.document_id as "Document ID",
cmsdw_activity_meta.activity_name as "Activity Name",
cmsdw_document.title as "Title",
cmsdw_document.creation_ts as "Creation Timestamp",
cmsdw_document.modification_ts as "Modification Timestamp",
cmsdw_user.firstname as "First Name",
cmsdw_user.lastname as "Last Name",
cmsdw_container.name as "Name",
cmsdw_document_stats_fact.content_id as "Content ID",
cmsdw_document_stats_fact.views as "Views",
cmsdw_document_stats_fact.likes as "Likes",
cmsdw_document_stats_fact.bookmarks as "Bookmarks",
cmsdw_document_stats_fact.comments as "Comments",
cmsdw_document_stats_fact.shares as "Shares",
cmsdw_document_stats_fact.unique_viewers as "Unique Viewers"
FROM
public.cmsdw_document,
public.cmsdw_document_stats_fact,
public.cmsdw_container,
public.cmsdw_object,
public.cmsdw_user,
public.cmsdw_activity_fact,
public.cmsdw_activity_meta
WHERE
cmsdw_activity_fact.activity_type = cmsdw_activity_meta.activity_type AND
cmsdw_document_stats_fact.content_id = cmsdw_object.object_id AND
cmsdw_document.document_id = cmsdw_object.object_id AND
cmsdw_container.container_id = cmsdw_document.container_id AND
cmsdw_object.dw_object_id = cmsdw_activity_fact.direct_dw_object_id AND
cmsdw_object.object_type = cmsdw_activity_fact.direct_object_type AND
cmsdw_activity_fact.user_id = cmsdw_user.user_id AND
cmsdw_container.name = 'Getting Started' AND
cmsdw_object.object_type = 102 AND
cmsdw_activity_fact.activity_type = 20;

Answer 1

You should fix your query to have proper join syntax -- simple rule: never use commas in the from clause.
For your query, you can replace the select with with:
select distinct on (cmsdw_document.document_id) . . .
The ". . ." is the rest of your query. Then add:
order by cmsdw_document.document_id, cmsdw_document.modification_ts desc
This should give you the latest document, using a Postgres extension.