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CTXCAT New Index Type
---------------------
This section discusses the limitations of using the new CTXCAT index type.
It also discusses the system parameters associated with this index type.
For a complete example of how to use CTXCAT, see Chapter 1 of the
Documentation Addendum.
Parameter String Limitations
----------------------------
To create a CTXCAT index, you use CREATE INDEX and optionally
specify preferences in the parameter string like you do when you
create a context index.
However, the keywords you can use in a ctxcat parameter string are limited to:
INDEX SET
LEXER
MEMORY
STOPLIST
STORAGE
WORDLIST
CTXCAT Supported Column Types
-----------------------------
The index set can take up to 99 indexes, each made up of ordered lists of
columns from the base table. However, there are two important restrictions
on these columns:
1. only allowable types are NUMBER, DATE, and CHAR/VARCHAR2 with maximum
length <= 30 bytes
2. NULL values are not allowed. A NULL in a user column will cause an
index error and the row will not be indexed.
CATSEARCH structured_query Parameter Limitations
------------------------------------------------
The following restrictions hold for the structured_query parameter
for the CATSEARCH operator:
* The left-hand side (the column name) must be a column named in
at least one of the indexes of the index set
* The left-hand side must be a plain column name -- no functions,
expressions, etc.
* The operator is limited to: <, <=, =, >=, >, BETWEEN, and IN
* The right-hand side must be composed of literal values -- no functions,
expressions, other columns, subselects, etc.
* Multiple criteria can be combined with AND. OR is not supported.
So all these are supported:
catsearch(text, 'dog', 'foo > 15')
catsearch(text, 'dog', 'bar = ''SMITH''')
catsearch(text, 'dog', 'foo between 1 and 15')
catsearch(text, 'dog', 'foo = 1 and abc = 123')
And these are NOT supported:
catsearch(text, 'dog', 'upper(bar) = ''A''')
catsearch(text, 'dog', 'bar LIKE ''A%''')
catsearch(text, 'dog', 'foo = abc')
catsearch(text, 'dog', 'foo = 1 or abc = 3')
CTXCAT System Parameters
------------------------
The catalog index has its own set of system parameters for setting
preference defaults. This allows an installation to have one set of
default preferences for context indexes, and another set for ctxcat
indexes. The new system parameters are:
DEFAULT_CTXCAT_LEXER
DEFAULT_CTXCAT_STOPLIST
DEFAULT_CTXCAT_WORDLIST
DEFAULT_CTXCAT_STORAGE
DEFAULT_CTXCAT_INDEX_SET
While you can specify a wordlist preference for ctxcat indexes, most of
the attributes do not apply, since the catsearch query language does not
support wildcarding, fuzzy, and stemming. The only attribute of the wordlist
preference that is useful is PREFIX_INDEX, for Japanese data.
