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Configure and Manage Stopwords and Stoplists for Full-Text Search

  • Artikkeli

Applies to: SQL Server Azure SQL Database

To prevent a full-text index from becoming bloated, SQL Server has a mechanism that discards commonly occurring strings that do not help the search. These discarded strings are called stopwords. During index creation, the Full-Text Engine omits stopwords from the full-text index. This means that full-text queries will not search on stopwords.

Stopwords. A stopword can be a word with meaning in a specific language. For example, in the English language, words such as "a," "and," "is," and "the" are left out of the full-text index since they are known to be useless to a search. A stopword can also be a token that does not have linguistic meaning.

Stoplists. Stopwords are managed in databases using objects called stoplists. A stoplist is a list of stopwords that, when associated with a full-text index, is applied to full-text queries on that index.

Use an existing stoplist

You can use an existing stoplist in the following ways:

  • Use the system-supplied stoplist in the database. SQL Server ships with a system stoplist that contains the most commonly used stopwords for each supported language, that is for every language associated with given word breakers by default. You can copy the system stoplist and customize your copy by adding and removing stopwords.

    The system stoplist is installed in the Resource database.

  • Use an existing custom stoplist from another database in the current server instance, then add or drop stopwords as appropriate.

Create a new stoplist

Create a new stoplist with Transact-SQL

Use CREATE FULLTEXT STOPLIST.

Create a new stoplist with Management Studio

  1. In Object Explorer, expand the server.

  2. Expand Databases, and then expand the database in which you want to create the full-text stoplist.

  3. Expand Storage, and then right-click Full-Text Stoplists.

  4. Select New Full-Text Stoplist.

  5. Enter your new stoplist's name.

  6. Optionally, specify someone else as the stoplist owner.

  7. Select one of the following create stoplist options:

    • Create an empty stoplist

    • Create from the system stoplist

    • Create from an existing full-text stoplist

    For more information, see New Full-Text Stoplist (General Page).

  8. Select OK.

Use a stoplist in full-text queries

To use a stoplist in queries, you must associate it with a full-text index. You can attach a stoplist to a full-text index when you create the index, or you can alter the index later to add a stoplist.

Create a full-text index and associate a stoplist with it

Use CREATE FULLTEXT INDEX (Transact-SQL).

Associate or disassociate a stoplist with an existing full-text index

Use ALTER FULLTEXT INDEX (Transact-SQL).

Change the stopwords in a stoplist

Add or drop stopwords from a stoplist with Transact-SQL

Use ALTER FULLTEXT STOPLIST (Transact-SQL).

Add or drop stopwords from a stoplist with Management Studio

  1. In Object Explorer, expand the server.

  2. Expand Databases, and then expand the database.

  3. Expand Storage, and then select Full Text Stoplists.

  4. Right-click the stoplist whose properties you want to change, and select Properties.

  5. In the Full-Text Stoplist Properties dialog box:

    1. In the Action list box, select one of the following actions: Add stopword, Delete stopword, Delete all stopwords, or Clear stoplist.

    2. If the Stopword text box is enabled for the selected action, enter a single stopword. This stopword must be unique; that is, not yet in this stoplist for the language that you select.

    3. If the Full-text language list box is enabled for the selected action, select a language.

  6. Select OK.

Manage stoplists and their usage

View all the stopwords in a stoplist

Use sys.fulltext_stopwords (Transact-SQL).

Get info about all the stoplists in the current database

Use sys.fulltext_stoplists (Transact-SQL) and sys.fulltext_stopwords (Transact-SQL).

View the tokenization result of a word breaker, thesaurus, and stoplist combination

Use sys.dm_fts_parser (Transact-SQL).

Suppress an error message if stopwords cause a Boolean operation on a full-text query to fail

Use the transform noise words Server Configuration Option.

More info about stopword position

Although it ignores the inclusion of stopwords, the full-text index does take into account their position. For example, consider the phrase, "Instructions are applicable to these Adventure Works Cycles models". The following table depicts the position of the words in the phrase:

Word Position
Instructions 1
are 2
applicable 3
to 4
these 5
Adventure 6
Works 7
Cycles 8
models 9

The stopwords "are", "to", and "these" that are in positions 2, 4, and 5 are left out of the full-text index. However, their positional information is maintained, thereby leaving the position of the other words in the phrase unaffected.

Upgrade noise words from SQL Server 2005

SQL Server 2005 (9.x) noise words have been replaced by stopwords. When a database is upgraded from SQL Server 2005 (9.x), the noise-word files are no longer used. However, the noise-word files are stored in the FTDATA\ FTNoiseThesaurusBak folder, and you can use them later when updating or building the corresponding stoplists. For information about upgrading noise-word files to stoplists, see Upgrade Full-Text Search.