FREETEXTTABLE (Transact-SQL)

Artikel
02/28/2023

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

Is a function used in the FROM clause of a Transact-SQL SELECT statement to perform a SQL Server full-text search on full-text indexed columns containing character-based data types. This function returns a table of zero, one, or more rows for those columns containing values that match the meaning and not just the exact wording, of the text in the specified freetext_string. FREETEXTTABLE is referenced as if it were a regular table name.

FREETEXTTABLE is useful for the same kinds of matches as the FREETEXT (Transact-SQL),

Queries using FREETEXTTABLE return a relevance ranking value (RANK) and full-text key (KEY) for each row.

Note

For information about the forms of full-text searches that are supported by SQL Server, see Query with Full-Text Search.

Transact-SQL syntax conventions

Syntax

FREETEXTTABLE (table , { column_name | (column_list) | * }   
          , 'freetext_string'   
     [ , LANGUAGE language_term ]   
     [ , top_n_by_rank ] )

Arguments

table
Is the name of the table that has been marked for full-text querying. table or viewcan be a one-, two-, or three-part database object name. When querying a view, only one full-text indexed base table can be involved.

table cannot specify a server name and cannot be used in queries against linked servers.

column_name
Is the name of one or more full-text indexed columns of the table specified in the FROM clause. The columns can be of type char, varchar, nchar, nvarchar, text, ntext, image, xml, varbinary, or varbinary(max).

column_list
Indicates that several columns, separated by a comma, can be specified. column_list must be enclosed in parentheses. Unless language_term is specified, the language of all columns of column_list must be the same.

*
Specifies that all columns that have been registered for full-text searching should be used to search for the given freetext_string. Unless language_term is specified, the language of all full-text indexed columns in the table must be the same.

freetext_string
Is text to search for in the column_name. Any text, including words, phrases or sentences, can be entered. Matches are generated if any term or the forms of any term is found in the full-text index.

Unlike in the CONTAINS search condition where AND is a keyword, when used in freetext_string the word 'and' is considered a noise word, or stopword, and will be discarded.

Use of WEIGHT, FORMSOF, wildcards, NEAR and other syntax is not allowed. freetext_string is wordbroken, stemmed, and passed through the thesaurus.

LANGUAGE language_term
Is the language whose resources will be used for word breaking, stemming, and thesaurus and stopword removal as part of the query. This parameter is optional and can be specified as a string, integer, or hexadecimal value corresponding to the locale identifier (LCID) of a language. If language_term is specified, the language it represents will be applied to all elements of the search condition. If no value is specified, the column full-text language is used.

If documents of different languages are stored together as binary large objects (BLOBs) in a single column, the locale identifier (LCID) of a given document determines what language is used to index its content. When querying such a column, specifying LANGUAGE language_term can increase the probability of a good match.

When specified as a string, language_term corresponds to the alias column value in the sys.syslanguages (Transact-SQL) compatibility view. The string must be enclosed in single quotation marks, as in 'language_term'. When specified as an integer, language_term is the actual LCID that identifies the language. When specified as a hexadecimal value, language_term is 0x followed by the hexadecimal value of the LCID. The hexadecimal value must not exceed eight digits, including leading zeros.

If the value is in double-byte character set (DBCS) format, Microsoft SQL Server will convert it to Unicode.

If the language specified is not valid or there are no resources installed that correspond to that language, SQL Server returns an error. To use the neutral language resources, specify 0x0 as language_term.

top_n_by_rank
Specifies that only the nhighest ranked matches, in descending order, are returned. Applies only when an integer value, n, is specified. If top_n_by_rank is combined with other parameters, the query could return fewer rows than the number of rows that actually match all the predicates. top_n_by_rank allows you to increase query performance by recalling only the most relevant hits.

Remarks

Full-text predicates and functions work on a single table, which is implied in the FROM predicate. To search on multiple tables, use a joined table in your FROM clause to search on a result set that is the product of two or more tables.

FREETEXTTABLE uses the same search conditions as the FREETEXT predicate.

Like CONTAINSTABLE, the table returned has columns named KEY and RANK, which are referenced within the query to obtain the appropriate rows and use the row ranking values.

Permissions

FREETEXTTABLE can be invoked only by users with appropriate SELECT privileges for the specified table or the referenced columns of the table.

Examples

A. Simple Example

The following example creates and populates a simple table of two columns, listing 3 counties and the colors in their flags. The it creates and populates a full-text catalog and index on the table. Then the FREETEXTTABLE syntax is demonstrated.

CREATE TABLE Flags (Country nvarchar(30) NOT NULL, FlagColors varchar(200));  
CREATE UNIQUE CLUSTERED INDEX FlagKey ON Flags(Country);  
INSERT Flags VALUES ('France', 'Blue and White and Red');  
INSERT Flags VALUES ('Italy', 'Green and White and Red');  
INSERT Flags VALUES ('Tanzania', 'Green and Yellow and Black and Yellow and Blue');  
SELECT * FROM Flags;  
GO  
  
CREATE FULLTEXT CATALOG TestFTCat;  
CREATE FULLTEXT INDEX ON Flags(FlagColors) KEY INDEX FlagKey ON TestFTCat;  
GO   
  
SELECT * FROM Flags;  
SELECT * FROM FREETEXTTABLE (Flags, FlagColors, 'Blue');  
SELECT * FROM FREETEXTTABLE (Flags, FlagColors, 'Yellow');

B. Using FREETEXT in an INNER JOIN

The following example returns the description and rank of any products with a description that matches the meaning of high level of performance.

USE AdventureWorks2022;  
GO  
  
SELECT FT_TBL.Description  
    ,KEY_TBL.RANK  
FROM Production.ProductDescription AS FT_TBL   
    INNER JOIN FREETEXTTABLE(Production.ProductDescription,  
    Description,   
    'high level of performance') AS KEY_TBL  
ON FT_TBL.ProductDescriptionID = KEY_TBL.[KEY]  
ORDER BY RANK DESC;  
GO

C. Specifying Language and Highest Ranked Matches

The following example is identical and shows the use of the LANGUAGElanguage_term and top_n_by_rank parameters.

USE AdventureWorks2022;  
GO  
  
SELECT FT_TBL.Description  
    ,KEY_TBL.RANK  
FROM Production.ProductDescription AS FT_TBL   
    INNER JOIN FREETEXTTABLE(Production.ProductDescription,  
    Description,   
    'high level of performance',  
    LANGUAGE N'English', 2) AS KEY_TBL  
ON FT_TBL.ProductDescriptionID = KEY_TBL.[KEY]  
ORDER BY RANK DESC;  
GO

Note

The LANGUAGE language_term parameter is not required to use the top_n_by_rank parameter.

Delen via