Oracle 5.0, Reference Manual

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Full-Text Restrictions
944
way we we'd we'll we're
we've welcome well went were
weren't what what's whatever when
whence whenever where where's whereafter
whereas whereby wherein whereupon wherever
whether which while whither who
who's whoever whole whom whose
why will willing wish with
within without won't wonder would
wouldn't yes yet you you'd
you'll you're you've your yours
yourself yourselves zero
12.9.5. Full-Text Restrictions
• Full-text searches are supported for
MyISAM
tables only.
• Full-text searches can be used with most multi-byte character sets. The exception is that for
Unicode, the
utf8
character set can be used, but not the
ucs2
character set. However, although
FULLTEXT
indexes on
ucs2
columns cannot be used, you can perform
IN BOOLEAN MODE
searches on a
ucs2
column that has no such index.
• Ideographic languages such as Chinese and Japanese do not have word delimiters. Therefore, the
FULLTEXT
parser cannot determine where words begin and end in these and other such languages.
The implications of this and some workarounds for the problem are described in Section 12.9, “Full-
Text Search Functions” .
• Although the use of multiple character sets within a single table is supported, all columns in a
FULLTEXT
index must use the same character set and collation.
• The
MATCH()
[934] column list must match exactly the column list in some
FULLTEXT
index
definition for the table, unless this
MATCH()
[934] is
IN BOOLEAN MODE
. Boolean-mode searches
can be done on nonindexed columns, although they are likely to be slow.
• The argument to
AGAINST()
must be a string value that is constant during query evaluation. This
rules out, for example, a table column because that can differ for each row.
• Index hints are more limited for
FULLTEXT
searches than for non-
FULLTEXT
searches. See
Section 13.2.8.3, “Index Hint Syntax” .
12.9.6. Fine-Tuning MySQL Full-Text Search
MySQL's full-text search capability has few user-tunable parameters. You can exert more control over
full-text searching behavior if you have a MySQL source distribution because some changes require
source code modifications. See
Section 2.17, “Installing MySQL from Source” .
Note that full-text search is carefully tuned for the most effectiveness. Modifying the default behavior
in most cases can actually decrease effectiveness. Do not alter the MySQL sources unless you know
what you are doing.
Most full-text variables described in this section must be set at server startup time. A server restart is
required to change them; they cannot be modified while the server is running.
Some variable changes require that you rebuild the
FULLTEXT
indexes in your tables. Instructions for
doing so are given later in this section.