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Query help to for min date with

Posted on 2011-02-10
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Last Modified: 2012-08-13
I have one table ...  (simplified here) ....   3 columns:
PLOT_VISIT_CN           PLOT              DATE
        1                        Big_Sagen          1/1/1997
        2                        Big_Sagen          2/3/2001
        3                        Little_Boy            1/1/1997
        4                        Little_Boy          7/23/2002
        5                        Little_Boy          8/24/2003

I'm trying to write a query to show the minimum date but I need all three fields.
When using only Plot and Min(Date) ...  looks good, but when add PLOT_VISIT_CN the rows are unique so I get them all.

Trying to join the table on itself without much luck.  I should know how to do this but cannot get it to work ...   appreciate any help.
Thanks
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Question by:DoveTails
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7 Comments
 
LVL 4

Expert Comment

by:IceCode
ID: 34864483
Can I see one of the queries that doesn't work and maybe an example of what you expect the output to look like please?
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LVL 31

Expert Comment

by:Helen Feddema
ID: 34864488
The question is, minimum date for what?  If you add PLOT_VISIT_CN, you will get the minimum date for that ID, which is to say, all records (one date per ID).
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Expert Comment

by:Helen Feddema
ID: 34864497
The GroupBy field is the one for which you will get the minimum date.
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LVL 120

Expert Comment

by:Rey Obrero (Capricorn1)
ID: 34864512

select a.*
from table as a
inner join
(select min(b.[date]) as minDate, PLOT_VISIT_CN
 from table as b
 group by PLOT_VISIT_CN
) as c
on a.[date]=c.[minDate] and a.PLOT_VISIT_CN=c.PLOT_VISIT_CN
0
 
LVL 5

Author Comment

by:DoveTails
ID: 34864977
Thanks for the quick responses....I'll share some more info.  

I'm after the earliest date for the PLOT, but I also need the PLOT_VISIT_CN along with it.
End results would be
PLOT_VISIT_CN           PLOT              DATE
        1                        Big_Sagen          1/1/1997
        3                        Little_Boy            1/1/1997

This query returns the correct data but does not contain the plot_visit_cn:
   SELECT Min(plot_visits.DATE) AS MinOfDATE, plot_visits.PLOT
   FROM plot_visits
   GROUP BY plot_visits.PLOT;

When I add the plot_visit_cn to the query as follows...i'm getting too many results, as Helen pointed out, i'm getting the earliest date for the PLOT_VISIT_CN.... and I want earliest for PLOT.
   SELECT plot_visits.PLOT_VISIT_CN, plot_visits.PLOT, Min(plot_visits.Date) AS MinOfDATE
   FROM plot_visits
   GROUP BY plot_visits.PLOT_VISIT_CN, plot_visits.PLOT;

and thanks Capricorn1 though the query is returning by PLOT_VISIT_CN also....I've been trying similar queries and think that's the way to go.
I'm still trying.....
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LVL 120

Accepted Solution

by:
Rey Obrero (Capricorn1) earned 2000 total points
ID: 34865048
try this


select a.*
from plot_visits as a
inner join
(select min(b.[date]) as minDate, b.PLOT_VISIT_CN
 from plot_visits as b
 group by b.PLOT_VISIT_CN
) as c
on a.[date]=c.[minDate] and a.PLOT_VISIT_CN=c.PLOT_VISIT_CN
0
 
LVL 5

Author Closing Comment

by:DoveTails
ID: 34865224
Thanks to everyone for helping out and a special thanks to Capricorn1  .... I needed to modify the final suggested query but it helped me understand what to do.  Here's my final query:
SELECT a.plot_visit_cn, a.plot, a.date
FROM plot_visits AS a
INNER JOIN
   (select min(b.[date]) as minDate, PLOT
    from plot_visits as b
    group by PLOT
    )  AS c ON (a.[date] = c.[minDate]) AND (a.PLOT = c.PLOT);

Thanks again !!!!
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