如何查詢最大日期？ （PostgreSQL）

Question

使用PostgreSQL，我希望只能看到具有最新修改時間戳的文檔ID。我很難得到這個工作，並想知道如果有人有任何指針？

這裏是我當前的代碼：

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

您應該解決您的查詢有正確的語法join - 簡單的規則：永遠不要在from子句中使用逗號。

爲您查詢，您可以用替換select：

select distinct on (cmsdw_document.document_id) . . . 

的 「」是你的查詢的其餘部分。然後添加：

order by cmsdw_document.document_id, cmsdw_document.modification_ts desc 

這應該給你最新的文檔，使用Postgres擴展。