Friday, October 28, 2011

ORACLE SQL TUTORIAL: INDEX OVERVIEW PART 2



PART 1:  http://www.shareoracleapps.com/2011/10/oracle-sql-tutorial-index-part-1.html

continuation.....


HOW A TEXT QEURY WORKS?

When a function such as CONTAINS or CATSEARCH is used in query, the text portion of the query is processed by oracle text. The remainder of the query is processed just like a regular query within the database. The result of the text query processing and the regular query processing are merged to return a single set of records to the user.
SEARCHING FOR AN EXACT MATCH OF A WORD

The following queries will search for a word called ‘prperty’ whose score is greater than zero.

SQL> select * from books where contains(info, ‘property’) > 0;
SQL> select * from books where catsearch(info, ‘property’, null) > 0;

Suppose if you want to know the score of the ‘property’ in each book, if score values for individual searches range from 0 to 10 for each occurrence of the string within the text then use the score function.

SQL> select title, score(10) from books where contains(info, ‘property’, 10) > 0;

SEARCHING FOR AN EXACT MATCH OF MULTIPLE WORDS

The following queries will search for two words.

SQL> select * from books where contains(info, ‘property AND harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property AND harvests’, null) > 0;

Instead of using AND you could hae used an ampersand(&). Before using this method, set define off so the & character will not be seen as part of a variable name.

SQL> set define off
SQL> select * from books where contains(info, ‘property & harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property  harvests’, null) > 0;

The following queries will search for more than two words.

SQL> select * from books where contains(info, ‘property AND harvests AND workers’) > 0;
SQL> select * from books where catsearch(info, ‘property harvests workers’, null) > 0;

The following queries will search for either of the two words.

SQL> select * from books where contains(info, ‘property OR harvests’) > 0;

Instead of OR you can use a vertical line (|).
SQL> select * from books where contains(info, ‘property | harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property | harvests’, null) > 0;

In the following queries the ACCUM(accumulate) operator adds together the scores of the individual searches and compares the accumulated score to the threshold value.

SQL> select * from books where contains(info, ‘property ACCUM harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property ACCUM harvests’, null) > 0;

Instead of OR you can use a comma(,).

SQL> select * from books where contains(info, ‘property , harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property , harvests’, null) > 0;

In the following queries the MINUS operator subtracts the score of the second term’s search from the score of the first term’s search.

SQL> select * from books where contains(info, ‘property MINUS harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property NOT harvests’, null) > 0;

Instead of MINUS you can use – and instead of NOT you can use ~.

SQL> select * from books where contains(info, ‘property - harvests’) > 0;
SQL> select * from books where catsearch(info, ‘property ~ harvests’, null) > 0;

SEARCHING FOR AN EXACT MATCH OF A PHRASE

The following queries will search for the phrase. If the search phrase includes a reserved word within oracle text, the you must use curly braces ({}) to enclose text.

SQL> select * from books where contains(info, ‘transactions {and} finances’) > 0;
SQL> select * from books where catsearch(info, ‘transactions {and} finances’, null) > 0;

You can enclose the entire phrase within curly braces, in which case any reserved words within the phrase will be treated as part of the search criteria.

SQL> select * from books where contains(info, ‘{transactions and finances}’) > 0;
SQL> select * from books where catsearch(info, ‘{transactions and finances}’, null) > 0;

SEARCHING FOR WORDS THAT ARE NEAR EACH OTHER

The following queries will search for the words that are in between the search terms.

SQL> select * from books where contains(info, ‘workers NEAR harvests’) > 0;

Instead of NEAR you can use ;.

SQL> select * from books where contains(info, ‘workers ; harvests’) > 0;

In CONTEXT index queries, you can specify the maximum number of words between the search terms.

SQL> select * from books where contains(info, ‘NEAR((workers, harvests),10)’ > 0;

USING WILDCARDS DURING SEARCHES

You can use wildcards to expand the list of valid search terms used during your query. Just as in regular text-string wildcard processing, two wildcards are available.

%            -              percent sign; multiple-character wildcard
_             -              underscore; single-character wildcard

SQL> select * from books where contains(info, ‘worker%’) > 0;
SQL> select * from books where contains(info, ‘work___’) > 0;

SEARCHING FOR WORDS THAT SHARE THE SAME STEM

Rather than using wildcards, you can use stem-expansion capabilities to expand the list of text strings. Given the ‘stem’ of a word, oracle will expand the list of words to search for to include all words having the same stem. Sample expansions are show here.

Play        -              plays playing played playful

SQL> select * from books where contains(info, ‘$manage’) > 0;

SEARCHING FOR FUZZY MATCHES

A fuzzy match expands the specified search term to include words that are spelled similarly but that do not necessarily have the same word stem. Fuzzy matches are most helpful when the text contains misspellings. The misspellings can be either in the searched text or in the search string specified by the user during the query.

The following queries will not return anything because its search does not contain the word ‘hardest’.

SQL> select * from books where contains(info, ‘hardest’) > 0;

It does, however, contains the word ‘harvest’. A fuzzy match will return the books containing the word ‘harvest’ even though ‘harvest’ has a different word stem thant the word used as the search term.
                                                                   
To use a fuzzy match, precede the search term with a question mark, with no space between the question mark and the beginning of the search term.

SQL> select * from books where contains(info, ‘?hardest’) > 0;

SEARCHING FOR WORDS THAT SOUND LIKE OTHER WORDS

SOUNDEX, expands search terms based on how the word sounds. The SOUNDEX expansion method uses the same text-matching logic available via the SOUNDEX function in SQL.

To use the SOUNDEX option, you must precede the search term with an exclamation mark(!).

SQL> select * from books where contains(info, ‘!grate’) > 0;

INDEX SYNCHRONIZATION

When using CONTEXT indexes, you need to manage the text index contents; the text indexes are not updated when the base table is updated. When the table was updated, its text index is out of sync with the base table. To sync of the index, execute the SYNC_INDEX procedure of the CTX_DDL package.

SQL> exec CTX_DDL.SYNC_INDEX(‘book_index’);

INDEX SETS

Historically, problems with queries of text indexes have occurred when other criteria are used alongside text searches as part of the where clause. To improve the mixed query capability, oracle features index sets. The indexes within the index set may be structured relational columns or on text columns.

To create an index set, use the CTX_DDL package to create the index set and add indexes to it. When you create a text index, you can then specify the index set it belongs to.

SQL> exec CTX_DDL.CREATE_INDEX_SET(‘books_index_set’);

The add non-text indexes.

SQL> exec CTX_DDL.ADD_INDEX(‘books_index_set’, ‘title_index’);

Now create a CTXCAT text index. Specify ctxsys.ctxcat as the index type, and list the index set in the parameters clause.

SQL> create index book_index on books(info) indextype is ctxsys.ctxcat parameters(‘index set books_index_set’);

1 Responses to “ORACLE SQL TUTORIAL: INDEX OVERVIEW PART 2”

Sridevi K said...
October 8, 2016 at 12:57 AM

Regards
Sridevi Koduru (Senior Oracle Apps Trainer Oracleappstechnical.com)
LinkedIn profile - https://in.linkedin.com/in/sridevi-koduru-9b876a8b
Please Contact for One to One Online Training on Oracle Apps Technical, Financials, SCM, SQL, PL/SQL, D2K at training@oracleappstechnical.com | +91 - 9581017828.


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