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Introduction to Full-Text Search

Full-text search allows fast and flexible indexing for keyword-based query of text data stored in a Microsoft SQL Server database. In contrast to the LIKE predicate, which only works on character patterns, full-text queries perform linguistic searches against this data, by operating on words and phrases based on rules of a particular language.

In Microsoft SQL Server 2005, full-text search delivers enterprise search functionality. Significant enhancements in the areas of performance, manageability, and functionality deliver exceptional search capabilities for applications of any size.

The performance benefit of using full-text search can be best realized when querying against a large amount of unstructured text data. A LIKE query against millions of rows of text data can take minutes to return; whereas a full-text query can take only seconds or less against the same data, depending on the number of rows that are returned.

You can build full-text indexes on columns that contain char, varchar and nvarchar data. Full-text indexes can also be built on columns that contain formatted binary data, such as Microsoft Word documents, stored in a varbinary(max) or image column. You cannot use the LIKE predicate to query formatted binary data.

To create a full-text index on a table, the table must have a single, unique not null column. For example, consider a full-text index for the Document table in Adventure Works in which the DocumentID column is the primary key column. A full-text index indicates that the word "instructions" is found at word number 24 and word number 44 in the DocumentSummary column for the row associated with a DocumentID of 3. This index structure supports an efficient search for all items containing indexed words and advanced search operations, such as phrase searches and proximity searches. For more information, see Document Table (AdventureWorks).

When processing a full-text query, the search engine returns to SQL Server the key values of the rows that match the search criteria. If you want to use a full-text query to find the documents that include the word "instructions", the DocumentID values of 3, 4, 6, 7 and 8 are obtained from the full-text index. SQL Server then uses these keys to return the matching rows.

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