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4 table Join - Eliminate repeating rows

Posted on 2009-05-04
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Last Modified: 2012-05-06
I am trying to show customer name and address together with the products they purchased. Including product attributes (color etc.).
Example
Joe Rabbitte, 1- Hopper Ave,
1 - Wolly jumper - Red,
2 - Wolly Socks - white
(count removed for clarity)


This query works fine with the first two joins but returns the products twice in the products_column when the third join is added.

Joe Rabbitte, 1- Hopper Ave,
1- Wolly jumper - Red,
1- Wolly jumper - Red,
2- Wolly Socks - white,
2- Wolly Socks - white,

I'm stuck has anyone any ideas on what I am doing wrong?
SELECT customers_name, customers_telephone, 
GROUP_CONCAT(products_name, ' ', LEFT(products_options_values, 4) SEPARATOR ' - ') AS products_bought
FROM orders
LEFT JOIN orders_products ON orders.orders_id = orders_products.orders_id
LEFT JOIN cc ON orders_products.orders_id = cc.order_id
LEFT JOIN orders_products_attributes ON cc.order_id = orders_products_attributes.orders_id
WHERE cc.payment_status = 'completed' AND orders.orders_id >10000
 
GROUP BY customers_name

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Question by:fearialtog
4 Comments
 
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by:mahome
mahome earned 150 total points
ID: 24293661
This will happen if you have 2 rows in orders_products_attributes per order id.
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by:yousaftahir
yousaftahir earned 150 total points
ID: 24293761
use distinct to get the distinct rows.
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pellep earned 450 total points
ID: 24293943
Using "distinct" is an option, but keep in mind that it's a very, very expensive operation, especially in your case where you construct the result by formula and strings. Basically, it has the compare each row returned lexigraphically with the current list of results. If your query returns even a medium sized resultset, you will likely see a significant performance-impact.

Agreeing with mahome, it seems this is more of an issue of data than query. For some reason, there appears to be two (or more) rows in the orders_products_attributes table for each order, even if the rows represent the same data (assuming here that the products_options_values column comes from the orders_products_attributes table). Either this is not intended, in which case it should be fixed and your query should run fine. If it IS intended than you may end up having to use distinct or dropping the orders_products_attributes portion from the query.

This is one of the inherent downsides to a normalized model and this pattern of attributes storage you're using - it makes this type of query more problematic.
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by:fearialtog
ID: 31577487
Thank you all for your help
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