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<h1>8. SQL Reference</h1>
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<a href="#utf8notes4odbc" title="UTF-8 Implementation Notes For ODBC">UTF-8 Implementation Notes For ODBC</a>
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<h2>8.5. Wide Character Identifiers</h2>
<p>All Virtuoso schema columns are confined to 8-bit character fields. This will
remain for backwards compatibility and performance reasons, however, there
are two options available for support of non-ASCII identifier names as follows:</p>
<ul>
<li>
<p>Maintain an 8-bit system. Pass all 8-bit codes that enter the
system and read them back according to the current database character set.
This has the convenience of a 1-to-1 correspondence between the character
lengths of an identifier and their representation, so it's a subject to
like single character wildcards etc.</p>
<p>This works well only for languages that do have single bit encodings
(like western-european languages and cyrillic). But this does not work at
all for the far-east languages. It also depends on the database character
set and does not allow identifiers to be composed from multiple character
sets.</p>
</li>
<li>
<p>Store all identifiers as UTF-8 encoded unicode strings. This
would allow seamless storage and retrieval of ANY character within the unicode
character space. This, however, has the disadvantage of the varying character
length representation which should be taken into account when comparing identifier
names with LIKE.</p>
</li>
</ul>
<p>Virtuoso supports the above cases which are switchable through the
"SQL_UTF8_EXECS" = 1/0 flag in the [Client] section of the Virtuoso INI file.
Setting SQL_UTF8_EXECS = 1 enables UTF-8 identifier storage and retrieval,
whereas setting SQL_UTF8_EXECS = 0 disables it. The default setting is 0: disabled
for backwards compatible option.</p>
<div class="note">
<div class="notetitle">Note:</div>
<p>Once a non-ASCII identifier gets stored using a particular setting for
the "SQL_UTF8_EXECS" flag and the flag is subsequently changed this will
make the stored identifiers unreadable by normal means (but can be read
by special means).</p>
</div>
<p>When an SQL statement comes into the driver(s) it is expanded into unicode (using
either the current database character set if it is a narrow string like in
SQLExecDirect, or taking it verbatim as in SQLExecDirectW). The unicode
string is then encoded into UTF-8 passed to the SQL parser. The SQL parser knows
that it will receive UTF-8 so it takes that into account when parsing the
national character literals (N'<literal>') and the "normal" literals ('<literal>').
It will however return identifier names in UTF-8, these will then get stored into
the DBMS system tables or compared against them depending on the type of statement.</p>
<p>All returned identifiers will be translated from UTF-8 to Unicode when
returned to the client, so the client should never actually see the
UTF-8 encoding of the identifiers.</p>
<p>Representing a string in UTF-8 will not change the identifier parsing rules
or the SQL applications logic since the SQL special characters - like dot,
quote, space etc - are ASCII symbols and they will get represented as a
single byte sequence in UTF-8.</p>
<p>The upper/lower functions should be used with care when applied to identifiers:
they will get narrow strings in UTF-8, so applying an upper/lower to them may
cause damage to the UTF-8 encoding. That is why the identifiers should be
converted explicitly to wide strings using the charset_recode function,
changed to upper or lower case and then translated back to UTF-8 using the
charset_recode function again.</p>
<p>Using single character LIKE
patterns against identifiers stored as narrow strings in system tables will generally not work, as a single character
may be represented with up to 6 bytes in UTF-8. An exception to that is when
using single character pattern to match an ASCII character.</p>
<a name="utf8notes4odbc" />
<h3>8.5.1. UTF-8 Implementation Notes For ODBC</h3>
<p>All wide functions which do return an identifier, like SQLDescribeColW and
friends, will return the correct wide literal. For their narrow counterparts,
such as SQLDescribeCol, the UTF-8 string will first be converted to a wide
string and then to a narrow string using the current database character set.
However, an extension to the ODBC standard has been implemented instructing
all result set returning meta-data functions, such as SQLTables and SQLTablesW,
to return SQL_NVARCHAR instead of SQL_VARCHAR columns. This is not a problem
for most applications since all they do is to map the result to
SQL_C_CHAR on retrieval which will convert the wide string to the appropriate
narrow string inside the driver using the current database character set.
This will cause problems with narrow applications like MS Query, trying to get
identifiers not representable in the current narrow character set, because
all they will get is the "untranslatable char" mark (currently a question mark).</p>
<br />
<a name="utf8notes4jdbc" />
<h3>8.5.2. UTF-8 Implementation Notes In JDBC</h3>
<p>Since JAVA is all unicode there are no unavoidable deviations from the JDBC
standard. However when printing the Java strings to the screen or a file
or getting their byte representation, the usual JAVA conversion rules apply.
The types of the meta data result set columns in JDBC are somewhat debatable,
but since they are usually retrieved with Resultset.getString() the Virtuoso
JDBC driver will return the raw wide string instead of trying to make it
VARCHAR before returning it to the application.</p>
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