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POMySQL String search and where clause condition order
 

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    <p>I'm working with large number of rows in db(MySQL, innoDb engine, approx 20 milion rows) and I need to perform fuzzy like searching quite a lot. For some reasons I decided to use jaro_winkler algorithm and for performance issues I implemented it as a function in SQL. Application is written in Python and there is a weird situation I came across today:</p> <p>Comparing these two queries (called from mysql shell not via Orm or etc):</p> <pre><code>SELECT * FROM products WHERE jaro_winkler(code, '78-1747') &gt; 0.7 AND code LIKE '%78%'; </code></pre> <p>and</p> <pre><code>SELECT * FROM products WHERE code LIKE '%78%' AND jaro_winkler(code, '78-1747') &gt; 0.7; </code></pre> <p>I noticed that first one is at least 10 times slower than the second one. It seems logical at first, but as I checked the order of conditions in WHERE should not matter.</p> <p>So my question - is it the normal behaviour ?</p> <p>And has someone (from practical experience) can recommend a best algorithm or function to perform fuzzy searching ? I know about damerau-levenshtein metric, but it turns to be slower than my current solution.</p> <p>EDIT: After using explain:</p> <p>I created sample database really quickly and used both queries:</p> <p>for the first query:</p> <pre><code>id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE products ALL NULL NULL NULL NULL 4166 Using where </code></pre> <p>query time: ~ 2 seconds</p> <p>explain for the second query:</p> <pre><code>id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE products ALL NULL NULL NULL NULL 4332 Using where </code></pre> <p>query time: ~ 0.1 second</p>
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    1. USMrLore
    1. USloleknwn
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    1. COAs pointed in this answer : http://dba.stackexchange.com/a/1794 you should try to use `EXPLAIN` to see if there's a difference between both queries
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      1. USkoopajah
    2. COOrder of conditions in a where clause should't matter, would be a better description of affairs. As in "This should work" is not "This will work" Explain will tell you what's going on
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      1. USTony Hopkinson
    3. COI put results of explain in first post.
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      1. USloleknwn
 

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