SCORE

The SCORE function searches a text search index using criteria that are specified in a search argument and returns a relevance score that measures how well a document matches the query.

search-argument-options

Notes:

¹ The same clause must not be specified more than once.

column-name

Specifies a qualified or unqualified name of a column that has a text search index that is to be searched. The column must exist in the table or view that is identified in the FROM clause in the statement and the column of the table, or the column of the underlying base table of the view must have an associated text search index. The underlying expression of the column of a view must be a simple column reference to the column of an underlying table, either directly or through another nested view.

search-argument

An expression that returns a character-string data type or graphic-string data type that contains the terms to be searched for. It must not be the empty string or contain all blanks. The actual length of the string must not exceed 32 740 bytes after conversion to Unicode and must not exceed the text search limitations or number of terms as specified in the search argument syntax. For information on search-argument syntax, see Text search argument syntax.

search-argument-options

A character string or graphic string value that specifies the search argument options to use for the search. It must be a constant or a variable.

The options that can be specified as part of the search-argument-options are:

QUERYLANGUAGE = value: Specifies the language value. The value can be any of the supported language codes. If QUERYLANGUAGE is not specified, the default is the language value of the text search index that is used when the function is invoked. If the language value of the text search index is AUTO, the default value for QUERYLANGUAGE is en_US. For more information on the query language option, see Text search language options.
RESULTLIMIT = value: Specifies the maximum number of results that are to be returned from the underlying search engine. The value must be an integer from 1 to 2 147 483 647. If RESULTLIMIT is not specified, no result limit is in effect for the query.
SCORE may or may not be called for each row of the result table, depending on the plan that the optimizer chooses. If SCORE is called once for the query to the underlying search engine, a result set of all of the ROWIDs or primary keys that match are returned from the search engine. This result set is then joined to the table containing the column to identify the result rows. In this case, the RESULTLIMIT value acts like a FETCH FIRST n ROWS ONLY from the underlying text search engine and can be used as an optimization. If SCORE is called for each row of the result because the optimizer determines that is the best plan, then the RESULTLIMIT option has no effect.

SYNONYM = OFF or SYNONYM = ON

Specifies whether to use a synonym dictionary associated with the text search index. The default is OFF.

OFF: Do not use a synonym dictionary.
ON: Use the synonym dictionary associated with the text search index.

If search-argument-options is the empty string or the null value, the function is evaluated as if search-argument-options were not specified.

The result of the function is a double-precision floating-point number. If search-argument can be null, the result can be null; if search-argument is null, the result is the null value.

The result of SCORE is a value between 0 and 1. The more frequent the column contains a match for the search criteria specified by search-argument, the larger the result value. If a match is not found, the result is 0. If the column value is null or search-argument contains only blanks or is the empty string, the result is 0.

SCORE is a non-deterministic function.

Notes

Prerequisites: In order to use the CONTAINS and SCORE functions, OmniFind Text Search Server for DB2® for i must be installed and started.

Rules: If a view, nested table expression, or common table expression provides a text search column for a CONTAINS or SCORE scalar function and the applicable view, nested table expression, or common table expression has a DISTINCT clause on the outermost SELECT, the SELECT list must contain all the corresponding key fields of the text search index.

If a view, nested table expression, or common table expression provides a text search column for a CONTAINS or SCORE scalar function, the applicable view, nested table expression, or common table expression cannot have a UNION, EXCEPT, or INTERSECT at the outermost SELECT.

If a common table expression provides a text search column for a CONTAINS or SCORE scalar function, the common table expression cannot be subsequently referenced again in the entire query unless that reference does not provide a text search column for a CONTAINS or SCORE scalar function.

CONTAINS and SCORE scalar functions are not allowed if the query specifies:

a distributed table,
a table with a read trigger, or
a logical file built over multiple physical file members.

Example

The following statement generates a list of employees in the order of how well their resumes match the query "programmer AND (java OR cobol)", along with a relevance value that is normalized between 0 (zero) and 100.
```
  SELECT EMPNO, INTEGER(SCORE(RESUME, 'programmer AND
    (java OR cobol)') * 100) AS RELEVANCE
    FROM EMP_RESUME
    WHERE RESUME_FORMAT = 'ascii'
    AND CONTAINS(RESUME, 'programmer AND (java OR cobol)') = 1
    ORDER BY RELEVANCE DESC
```
The database manager first evaluates the CONTAINS predicate in the WHERE clause, and therefore, does not evaluate the SCORE function in the SELECT list for every row of the table. In this case, the arguments for SCORE and CONTAINS must be identical.