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Find Key Phrases in Documents with Semantic Search

 

Applies To: SQL Server 2016

Describes how to find the key phrases in documents or text columns that are configured for statistical semantic indexing.

How to: Find the Key Phrases in Documents with SEMANTICKEYPHRASETABLE

To identify the key phrases in specific documents, or to identify documents that contain specific key phrases, query the function semantickeyphrasetable (Transact-SQL).

SEMANTICKEYPHRASETABLE returns a table with zero, one, or more rows for those key phrases associated with columns in the specified table. This rowset function can be referenced in the FROM clause of a SELECT statement as if it were a regular table name.

System_CAPS_ICON_note.jpg Note


In SQL Server 2016, only single words are indexed for semantic search; multi-word phrases (ngrams) are not indexed. Also, various forms of the same word are indexed separately; for example, "computer" and "computers" are indexed separately.

For detailed information about the parameters required by the SEMANTICKEYPHRASETABLE function, and about the table of results that it returns, see semantickeyphrasetable (Transact-SQL).

System_CAPS_ICON_important.jpg Important


The columns that you target must have full-text and semantic indexing enabled.

Example 1: Find the Top Key Phrases in a Specific Document

The following example retrieves the top 10 key phrases from the document specified by the @DocumentId variable in the Document column of the Production.Document table of the AdventureWorks sample database. The @DocumentId variable represents a value from the key column of the full-text index.

SELECT TOP(10) KEYP_TBL.keyphrase  
FROM SEMANTICKEYPHRASETABLE  
    (  
    Production.Document,  
    Document,  
    @DocumentId  
    ) AS KEYP_TBL  
ORDER BY KEYP_TBL.score DESC;  
GO  

The SEMANTICKEYPHRASETABLE function retrieves these results efficiently by using an index seek instead of a table scan.

Example 2: Find the Top Documents that Contain a Specific Key Phrase

The following example retrieves the top 25 documents that contain the key phrase “Bracket” from the Document column of the Production.Document table of the AdventureWorks sample database.

SELECT TOP (25) DOC_TBL.DocumentID, DOC_TBL.DocumentSummary  
FROM Production.Document AS DOC_TBL  
    INNER JOIN SEMANTICKEYPHRASETABLE  
    (  
    Production.Document,  
    Document  
    ) AS KEYP_TBL  
ON DOC_TBL.DocumentID = KEYP_TBL.document_key  
WHERE KEYP_TBL.keyphrase = 'Bracket'  
ORDER BY KEYP_TBL.Score DESC;  
GO  

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