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POWhy do SQL FullText queries slow down when you OR?
 

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  1. POWhy do SQL FullText queries slow down when you OR?
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    <p>In SQL Server (2008), I have a FullText index on two columns, call them <code>Table1.FirstNames</code> and <code>Table2.LastNames</code>. After profiling some queries, I came up with the following results:</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE CONTAINS(FirstNames, 'Bob') OR CONTAINS(LastNames, 'Bob') </code></pre> <p>=> 31 197ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE (FirstNames LIKE '%Bob%') OR CONTAINS(LastNames, 'Bob') </code></pre> <p>=> 1941ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE CONTAINS(FirstNames, 'Bob') OR LastNames LIKE '%Bob%' </code></pre> <p>=> 3201ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE CONTAINS(FirstNames, 'Bob') </code></pre> <p>=> 565ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE FirstNames LIKE '%Bob%' </code></pre> <p>=> 670ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE CONTAINS(LastNames, 'Bob') </code></pre> <p>=> 17ms</p> <pre><code>SELECT * FROM (Table1 LEFT JOIN Table2 ON Table1.SomeKey=Table2.SomeKey) WHERE LastNames LIKE '%Bob%' </code></pre> <p>=> 3ms</p> <p>This behaviour persists even if I rebuild the FullText index.</p> <p>FullText is usually much faster than a LIKE query over large sets of data in a specific language, but why do query speeds slow down by an order of magnitude when I OR together two FullText clasues?</p>
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    1. USAndrew Song
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    1. COHow well does `WHERE FirstNames Like '%Bob%' OR LastNames Like '%Bob%'` work?
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      1. USRobert Harvey
    2. COAbout 2 seconds (I'm working with him on this)
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