Обсуждение: removing duplicates and using sort

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removing duplicates and using sort

От
Nathan Mailg
Дата:
I'm using 8.4.17 and I have the following query working, but it's not quite what I need:

SELECT DISTINCT ON (refid) id, refid, lastname, firstname, appldate
        FROM appl WHERE lastname ILIKE 'Williamson%' AND firstname ILIKE 'd%'
        GROUP BY refid, id, lastname, firstname, appldate ORDER BY refid, appldate DESC;

I worked on this awhile and is as close as I could get. So this returns rows as you'd expect, except I need to somehow modify this query so it returns the rows ordered by lastname, then firstname.

I'm using distinct so I get rid of duplicates in the table where refid (an integer) is used as the common id that ties like records together. In other words, I'm using it to get only the most recent appldate (a date) for each group of refid's that match the lastname, firstname where clause.

I just need the rows returned from the query above to be sorted by lastname, then firstname.

Hope I explained this well enough. Please let me know if you need more info.

Thanks!

Re: removing duplicates and using sort

От
"Edward W. Rouse"
Дата:

Change the order by to order by lastname, firstname, refid, appldate

 

From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of Nathan Mailg
Sent: Saturday, September 14, 2013 10:36 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] removing duplicates and using sort

 

I'm using 8.4.17 and I have the following query working, but it's not quite what I need:

 

SELECT DISTINCT ON (refid) id, refid, lastname, firstname, appldate
        FROM appl WHERE lastname ILIKE 'Williamson%' AND firstname ILIKE 'd%'
        GROUP BY refid, id, lastname, firstname, appldate ORDER BY refid, appldate DESC;

 

I worked on this awhile and is as close as I could get. So this returns rows as you'd expect, except I need to somehow modify this query so it returns the rows ordered by lastname, then firstname.

 

I'm using distinct so I get rid of duplicates in the table where refid (an integer) is used as the common id that ties like records together. In other words, I'm using it to get only the most recent appldate (a date) for each group of refid's that match the lastname, firstname where clause.

 

I just need the rows returned from the query above to be sorted by lastname, then firstname.

 

Hope I explained this well enough. Please let me know if you need more info.

 

Thanks!

Re: removing duplicates and using sort

От
David Johnston
Дата:
Note that you could always do something like:

WITH original_query AS (
SELECT DISTINCT ...
)
SELECT *
FROM original_query
ORDER BY lastname, firstname;

OR

SELECT * FROM (   SELECT DISTINCT ....
) sub_query
ORDER BY lastname, firstname

I am thinking you cannot alter the existing ORDER BY otherwise your use of
"DISTINCT ON" begins to mal-function.  I dislike DISTINCT ON generally but
do not wish to ponder how you can avoid it, so I'd suggest just turning your
query into a sub-query like I show above.

David J.




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Re: removing duplicates and using sort

От
Nathan Mailg
Дата:
Yes, that's correct, modifying the original ORDER BY gives:

ORDER BY lastname, firstname, refid, appldate DESC;
ERROR:  SELECT DISTINCT ON expressions must match initial ORDER BY expressions

Using WITH works great:

WITH distinct_query AS (   SELECT DISTINCT ON (refid) id, refid, lastname, firstname, appldate       FROM appl WHERE
lastnameILIKE 'Williamson%' AND firstname ILIKE 'd%'       GROUP BY refid, id, lastname, firstname, appldate
ORDERBY refid, appldate DESC   ) 
SELECT * FROM distinct_query ORDER BY lastname, firstname;

Thank you!