mysql - Query to delete old records, with an exception -


lets have table keeps history of prices, example:

 _______________________________________________________ |make  | model |  year  |  price  |    date_of_record   | |-------------------------------------------------------- |mazda |   6   |  2008  | 10,000  | 2013-05-13 00:00:00 | |mazda |   6   |  2008  | 11,000  | 2012-05-13 00:00:00 | |mazda |   6   |  2008  | 12,000  | 2011-05-13 00:00:00 | |mazda |   6   |  2008  | 11,750  | 2010-05-13 00:00:00 | |honda | civic |  2000  | 3,000   | 2011-05-13 00:00:00 | |honda | civic |  2000  | 4,000   | 2010-05-13 00:00:00 | |honda | civic |  2000  | 5,000   | 2009-05-13 00:00:00 | |honda | civic |  2000  | 5,050   | 2008-05-13 00:00:00 | |acura |   tl  |  2009  | 21,000  | 2010-05-13 00:00:00 | |--------------------------------------------------------

i want delete entries more 2 years old unless latest entry more 2 years old. hard put words, want end this:

 _______________________________________________________ |make  | model |  year  |  price  |    date_of_record   | |-------------------------------------------------------- |mazda |   6   |  2008  | 10,000  | 2013-05-13 00:00:00 | |mazda |   6   |  2008  | 11,000  | 2012-05-13 00:00:00 | |honda | civic |  2000  | 3,000   | 2011-05-13 00:00:00 | |acura |   tl  |  2009  | 21,000  | 2010-05-13 00:00:00 | |--------------------------------------------------------

so query delete entries more 2 years old mazda, , entries more 2 years old honda , acura, exception of latest.

entries inserted table when price changes, if price hasn't changed in 5 years entry 5 years old, not mean data not accurate.

first, lets list of car, make, model, year , respective latest "date of record". so, have 2007 vehicle , 2008 of same make/model each latest date entry of 2011-01-01. want keep vehicle entry both 2007 , 2008 models however, example showed old dates want keep retained data honda civic , acural tl respectively.

run this, confirm results

select        c.`make`,       c.`model`,       c.`year`,       max( c.date_of_record ) latestrecorddate           yourcarpricetable c    group       c.`make`,       c.`model`,       c.`year`    having       max( c.date_of_record ) < date_add(curdate(),interval -2 year)

now, use basis delete current table via left join on same make, model , year. 2 conditions allow delete.
1) there no match found in "keepthese" subquery , latest date of record more 2 years old...

2) there match found in "keepthese" subquery , date older recent qualified (too old) result set of keepthese.

per data example, "keepthese" result set should include

make   model   year   latestrecorddate honda  civic   2000   2011-05-13 00:00:00 acura  tl      2009   2010-05-13 00:00:00

so, mazda 6 delete 2 entries 2010 , 2011 date entries since make/model/year not included in list (via test null).

your honda civic delete entries older it's latest "keepthese" value of 2011-05-13, , delete 2008, 2009 , 2010 entries.

your acura tl not have older it's single entry, left alone.

delete ypt.*    yourcarpricetable ypt       left join ( select                          c.`make`,                         c.`model`,                         c.`year`,                         max( c.date_of_record ) latestrecorddate                                               yourcarpricetable c                      group                         c.`make`,                         c.`model`,                         c.`year`                      having                         max( c.date_of_record ) < date_add(curdate(),interval -2 year) ) keepthese          on ypt.`make` = keepthese.`make`          , ypt.`model` = keepthese.`model`          , ypt.`year` = keepthese.`year`          (     keepthese.`make` null         , ypt.date_of_record < date_add(curdate(),interval -2 year))       or       (      ypt.`make` = keepthese.`make`          , ypt.`model` = keepthese.`model`          , ypt.`year` = keepthese.`year`          , ypt.date_of_record < keepthese.latestrecorddate )

the subquery processed once front, left-joined delete version of car/price table.


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