How can I modify this query with two Inner Joins so that it stops giving duplicate results?

问题

EDIT: I will leave the post here as is, but what I really needed to accomplish needed to be reposted. I didn't explain the problem well enough. After trying again with quite a different starting point, I was able to get the query that I needed. That is explained here.

ORIGINAL QUESTION: I'm having trouble. I have looked at similar threads, and I am unable to find a solution specific to this query. The database is very large, and group by seems to slow it down immensely.

The problem is I am getting duplicate results. Here is my query which causes duplicates:

SELECT 
  itpitems.identifier, 
  itpitems.name, 
  itpitems.subtitle, 
  itpitems.description, 
  itpitems.itemimg, 
  itpitems.mainprice, 
  itpitems.upc, 
  itpitems.isbn, 
  itpitems.weight, 
  itpitems.pages, 
  itpitems.publisher, 
  itpitems.medium_abbr, 
  itpitems.medium_desc, 
  itpitems.series_abbr, 
  itpitems.series_desc, 
  itpitems.voicing_desc,
  itpitems.pianolevel_desc,
  itpitems.bandgrade_desc,
  itpitems.category_code,
  itprank.overall_ranking,
  itpitnam.name AS artist,
  itpitnam.type_code 
FROM itpitems 
  INNER JOIN itprank ON ( itprank.item_number = itpitems.identifier ) 
  INNER JOIN itpitnam ON ( itpitems.identifier = itpitnam.item_number ) 
WHERE mainprice >1

The results are actually not complete duplicates. itpitnam.type_code has a different result in the otherwise duplicated results.

Since adding GROUP BY to the end of the query is causing too much strain on the server (It's searching through about 300,000 records) what else can I do?

Can this be re-written as a sub-query? I just can't figure out how to eliminate the 2nd instances where type_code has changed.

Thank you for your help and assistance.

I also tried SELECT DISTINCT itpitems.identifier, but this served out the same results and had the duplicates (where type_code was the only difference). I don't want the second instance where type_code has changed. I just want one result per identifier regardless of whether or not type_code has multiple instances.

回答1:

Without seeing examples of the output, hard to say. But have you tried the same exact query with a simple DISTINCT added to the SELECT?

SELECT DISTINCT itpitems.identifier, itpitems.name, itpitems.subtitle, itpitems.description, itpitems.itemimg, itpitems.mainprice, itpitems.upc, itpitems.isbn, itpitems.weight, itpitems.pages, itpitems.publisher, itpitems.medium_abbr, itpitems.medium_desc, itpitems.series_abbr, itpitems.series_desc, itpitems.voicing_desc, itpitems.pianolevel_desc, itpitems.bandgrade_desc, itpitems.category_code, itprank.overall_ranking, itpitnam.name AS artist, itpitnam.type_code 
FROM itpitems 
INNER JOIN itprank ON ( itprank.item_number = itpitems.identifier ) 
INNER JOIN itpitnam ON ( itpitems.identifier = itpitnam.item_number ) 
WHERE mainprice >1

来源：https://stackoverflow.com/questions/14658033/how-can-i-modify-this-query-with-two-inner-joins-so-that-it-stops-giving-duplica

标签

mysql

group-by

subquery

inner-join