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POOptimize 5 table SQL query (stores => items => words)
 

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    <blockquote> <h1>Tables</h1> <p><strong>stores (100,000 rows)</strong>: id (pk), name, lat, lng, ...</p> <p><strong>store_items (9,000,000 rows)</strong>: store_id (fk), item_id (fk)</p> <p><strong>items (200,000 rows)</strong>: id(pk), name, ...</p> <p><strong>item_words (1,000,000 rows)</strong>: item_id(fk), word_id(fk)</p> <p><strong>words (50,000 rows)</strong>: id(pk), word VARCHAR(255)</p> </blockquote> <p>Note: all ids are integers.</p> <p>========</p> <blockquote> <h1>Indexes</h1> <p>CREATE UNIQUE INDEX storeitems_storeid_itemid_i ON store_items(store_id,item_id);</p> <p>CREATE UNIQUE INDEX itemwords_wordid_itemid_i ON item_words(word_id,item_id);</p> <p>CREATE UNIQUE INDEX words_word_i ON words(word);</p> </blockquote> <p>Note: I prefer multi column indexes (storeitems_storeid_itemid_i and itemwords_wordid_itemid_i) because: <a href="http://www.mysqlperformanceblog.com/2008/08/22/multiple-column-index-vs-multiple-indexes/" rel="nofollow">http://www.mysqlperformanceblog.com/2008/08/22/multiple-column-index-vs-multiple-indexes/</a></p> <h1>QUERY</h1> <pre><code>select s.name, s.lat, s.lng, i.name from words w, item_words iw, items i, store_items si, stores s where iw.word_id=w.id and i.id=iw.item_id and si.item_id=i.id and s.id=si.store_id and w.word='MILK'; </code></pre> <h2>Problem: elapsed time is 20-120 sec (depending on the word)!!!</h2> <pre><code>explain $QUERY$ +----+-------------+-------+--------+-------------------------------------------------------+-----------------------------+---------+-----------------------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+-------------------------------------------------------+-----------------------------+---------+-----------------------------+------+-------------+ | 1 | SIMPLE | w | const | PRIMARY,words_word_i | words_word_i | 257 | const | 1 | Using index | | 1 | SIMPLE | iw | ref | itemwords_wordid_itemid_i,itemwords_itemid_fk | itemwords_wordid_itemid_i | 4 | const | 1 | Using index | | 1 | SIMPLE | i | eq_ref | PRIMARY | PRIMARY | 4 | iw.item_id | 1 | | | 1 | SIMPLE | si | ref | storeitems_storeid_itemid_i,storeitems_itemid_fk | storeitems_itemid_fk | 4 | iw.item_id | 16 | Using index | | 1 | SIMPLE | s | eq_ref | PRIMARY | PRIMARY | 4 | si.store_id | 1 | | </code></pre> <h2>I want elapsed time to be less than 5 secs!!! Any ideas???</h2> <p>==============</p> <h1>What I tried</h1> <p>I tried to see when increase in the execution time happens by adding tables to the query.</p> <h2>1 table</h2> <pre><code>select * from words where word='MILK'; Elapsed time: 0.4 sec </code></pre> <h2>2 tables</h2> <pre><code>select count(*) from words w, item_words iw where iw.word_id=w.id and w.word='MILK'; Elapsed time: 0.5-2 sec (depending on word) </code></pre> <h2>3 tables</h2> <pre><code>select count(*) from words w, item_words iw, items i where iw.word_id=w.id and i.id=iw.item_id and w.word='MILK'; Elapsed time: 0.5-2 sec (depending on word) </code></pre> <h2>4 tables</h2> <pre><code>select count(*) from words w, item_words iw, items i, store_items si where iw.word_id=w.id and i.id=iw.item_id and si.item_id=i.id and w.word='MILK'; Elapsed time: 20-120 sec (depending on word) </code></pre> <p>I guess the problem with the indexes or with the design of query/database. But there must be a way to make it work fast. Google does it somehow and their tables are much bigger!</p>
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    1. CO**And I want cookies!**
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    2. CONo, seriously. We're not here to do work for you. If you have a specific question, feel free to ask it. If you want a code review, please go to [Code Review](http://codereview.stackexchange.com/). If you have a design question, please go to [Programmers](http://programmers.stackexchange.com/). But don't expect that any question which is like `I need [stuff], please do it for me` will be answered. You might also want to look at the [How To Ask A Question](http://stackoverflow.com/questions/how-to-ask)-Guide and the related topics.
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    3. COWhat is the data type of the word column? It seems the index is too big to fit in memory. Do you really need it to be unique field or you can create index on part of the field?
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      1. USMaxim Krizhanovsky
 

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