15.4.6. XCONTAINS predicate
This predicate is used in a SQL statement, it returns "true" if a free text indexed column with XML content matches an XPATH expression. Optionally produces the matching node set as a result set.
xcontains_pred: xcontains (column, expr [, result_var [, opt_or_value ...]]) opt_or_value: DESCENDING | START_ID ',' scalar_exp | END_ID ',' scalar_exp | SCORE_LIMIT ',' scalar_exp | OFFBAND column result_var: IDENTIFIER | NULL
The column must refer to a column for which there exists a free text index.
The expr must be a narrow or wide string expression whose syntax matches the rules in 'XPATH Query Syntax'.
The result_var variable is a query variable which, if present, will be successively bound to each element of the node set selected by the XPATH expression. if the value is not a node set and is true, the variable will be once bound to this value. The scope of the variable is the containing select and its value is a scalar or an XML entity. The result_var can be not an identifier but a NULL keyword to explicitly indicate that no query variable is required.
The START_ID is the first allowed document ID to be selected by the expression in its traversal order, e.g. least or equal for ascending and greatest or equal for descending.
END_ID is the last allowed id in the traversal order. For descending order the START_ID must be >= END_ID for hits to be able to exist. For ascending order the START_ID must be <= END_ID for hits to be able to exist.
DESCENDING specifies that the search will produce the hit with the greatest ID first, as defined by integer or composite collation. This has nothing to do with a possible ORDER BY of the enclosing statement. Even if there is an ORDER BY in the enclosing statement the DESCENDING keyword of xcontains has an effect in the interpretation of the STRT_ID and END_ID xcontains options.
RANGES specifies that the query variable following the RANGES keyword will be bound to the word position ranges of the hits of the expression inside the document. The variable is in scope inside the enclosing SELECT statement.
SCORE_LIMIT specifies a minimum score that hits must have or exceed to be considered matches of the predicate.
OFFBAND specifies that the following column will be retrieved from the free text index instead of the actual table. For this to be possible the column must have been declared as offband with the CLUSTERED WITH option of the CREATE TEXT INDEX statement.
If the select statement containing the xcontains predicate does not specify an exact match of the primary key of the table having the xcontains predicate, then the contains predicate will be the 'driving' condition, meaning that rows come in ascending or descending order of the free text document ID. If there is a full equality match of the primary key of the table, this will be the driving predicate and xcontains will only be used to check if the text expression matches the single row identified by the full match of the primary key.
The xcontains predicate may not appear outside of a select statement and may only reference a column for which a free text index has been declared. The first argument must be a column for which there is such an index. The text expression may be variable and computed, although it must be constant during the evaluation of the select statement containing it.
The xcontains predicate must be a part of the top level AND of the WHERE clause of the containing select. It may not for example be a term of an OR predicate in the select but can be AND'ed with an OR expression.
Example 15.13. Selecting Title Elements Called 'Key'
select xt_file from xml_text2 where xcontains (xt_text, '//title = "Key"');
The query retrieves the
xt_file for rows whose
xt_text is an XML document containing
'Key' as the text value of a title element.
If not all values in
xt_text are valid XMLs then '__quiet'
option can be useful to disable error signalling. It is unusual to
get an incorrect XML stored in a column that has free text XML
index because both on insert and on update the text is parsed by an
free text indexing routine, but the error is possible if e.g. a
non-standalone document is stored and an important external entity
was available at indexing time but disappeared later. Thus a
modified example might be better for a column with non-standalone
select xt_file from xml_text2 where xcontains (xt_text, '[__quiet] //title = "Key"');
Selecting Title Element that Contains a Specified Text
select n from xml_text2 where xcontains(xt_text, '//title[. = "AS Declaration - Column Aliasing"]',0,n);
The query retrieves each title element from each row of
xml_text2 where the
xt_text contains title
elements with the text value "AS Declaration - Column
The equality test is case- and whitespace-sensitive, as normal in XPath. The free text index is used for the search but the final test is done according to XPath rules.
The CONTAINS Predicate.