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我已经思考了相关的帖子，但无法获得成功。我需要一份报告，显示客户的最后一条注释。我真的很接近，但查询通常会“错过”实际的最后一个条目。假设我运行报告以显示过去 6 个月的最后一个条目，并将“bob”的最后一个条目显示为 8/1/13。当我查看表格时，有一个关于 10/23/13 的注释。我检查了数据是否以某种方式搞砸了，但看起来不错。如果有人能阐明为什么我在查询中有一些“几乎是最后的注释”而不是实际的最新注释，我将非常感激。这是我使用的查询和解释它的评论：

SELECT  
DISTINCT ON (c.client_id) --the client id
g.name, -- the office location
MAX (n.date_service),
n.date_creation, 
sv.code, -- the service / activity code
c.name_lastfirst_cs, -- client's name
n.date_service,  
s.staff_id -- staff id
FROM  notes n, clients c, services sv,  staff s, groups g
WHERE n.zrud_service = sv.zzud_service
AND n.visibility_flag = '1' -- 1 = valid note
AND n.zrud_client = c.zzud_client
AND n.zrud_staff = s.zzud_staff
AND n.zrud_group = g.zzud_group
AND g.name = 'HALIFAX' -- am specifying a single location

-- the next 4 lines were an attempt to query specific time range and actitity codes
--AND s.code IN ('10101', '10102', '10201',     10202','10203','10204','10205','10401','10402','10403','10405')
-- AND n.date_service >= '1/1/2010'
-- AND n.date_service<= '11/7/2013'
-- AND n.date_service BETWEEN (now() - '800 days'::interval)::timestamp AND now() 

GROUP BY g.name,sv.code, c.client_id, c.name_lastfirst_cs, s.staff_id,
n.date_service, n.date_creation
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1 回答 1

1

当您想要基于some_date表格的最后一个条目时，使用DISTINCT ONwithORDER BY some_date DESC是一个不错的选择：

SELECT  
DISTINCT ON (c.client_id) --the client id
g.name, -- the office location
n.date_service,
n.date_creation, 
sv.code, -- the service / activity code
c.name_lastfirst_cs, -- client's name
n.date_service,  
s.staff_id -- staff id
FROM  notes n, clients c, services sv,  staff s, groups g
WHERE n.zrud_service = sv.zzud_service
AND n.visibility_flag = '1' -- 1 = valid note
AND n.zrud_client = c.zzud_client
AND n.zrud_staff = s.zzud_staff
AND n.zrud_group = g.zzud_group
AND g.name = 'HALIFAX' -- am specifying a single location
ORDER BY c.client_id, n.date_service DESC;

请注意，不需要GROUP BYnor MAX，它只DISTINCT ON负责分组和ORDER BY检索最后一个条目。

于 2013-11-06T13:37:55.557 回答