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POHow are efficient consecutive word searches implemented?
 

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  1. POHow are efficient consecutive word searches implemented?
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    <p>Search engines and databases allow you to use consecutive string search (such as <code>"this is a test"</code>), which matches <code>this is a test that will match</code>, but won't match <code>test this is a</code>.</p> <p>I know that some databases have built-in features that allow you to use the same functionality without writing a single line of code (e.g. MySQL's full text search). That's not the kind of answer I am looking for.</p> <p>What I want to know is what kind of algorithm and database structures are used to enable this fast searching of strings.</p> <p>What would the indexed table look like given the above example? Would it be something similar to this?</p> <pre><code>// IndexedItemID | Position | Word 1 | 0 | this 1 | 1 | is 1 | 2 | a 1 | 3 | test 1 | 4 | that 1 | 5 | will 1 | 6 | match 2 | 0 | test 2 | 1 | this 2 | 2 | is 2 | 3 | a </code></pre> <p>Now that there are indexed items, how do you efficiently create a SQL statement that matches those items?</p> <p>Here's one example I can think of:</p> <pre><code>select IndexedItemID form (select IndexedItemID, Position from indexedWords where Word = "this") as word1Position where exists(select * from indexedWords where IndexedItemID = word1Position.IndexedItemID AND Word = "is" AND Position = word1Position.Position + 1) AND exists(select * from indexedWords where IndexedItemID = word1Position.IndexedItemID AND Word = "a" AND Position = word1Position.Position + 2) AND exists(select * from indexedWords where IndexedItemID = word1Position.IndexedItemID AND Word = "test" AND Position = word1Position.Position + 3) </code></pre> <p>I'm sure there is probably a more standardized way that's more efficient.</p>
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      1. POHow are efficient consecutive word searches implemented?
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    1. COMySQL's full text indexing is open source afaik, so download & find out :)
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