lower case, e.g.:
<programlisting>
UPDATE my_table SET a = 5;
</programlisting>
   </para>

   <para>
    <indexterm>
     <primary>quotation marks</primary>
     <secondary>and identifiers</secondary>
    </indexterm>
    There is a second kind of identifier:  the <firstterm>delimited
    identifier</firstterm> or <firstterm>quoted
    identifier</firstterm>.  It is formed by enclosing an arbitrary
    sequence of characters in double-quotes
    (<literal>"</literal>). <!-- " font-lock mania --> A delimited
    identifier is always an identifier, never a key word.  So
    <literal>"select"</literal> could be used to refer to a column or
    table named <quote>select</quote>, whereas an unquoted
    <literal>select</literal> would be taken as a key word and
    would therefore provoke a parse error when used where a table or
    column name is expected.  The example can be written with quoted
    identifiers like this:
<programlisting>
UPDATE "my_table" SET "a" = 5;
</programlisting>
   </para>

   <para>
    Quoted identifiers can contain any character, except the character
    with code zero.  (To include a double quote, write two double quotes.)
    This allows constructing table or column names that would
    otherwise not be possible, such as ones containing spaces or
    ampersands.  The length limitation still applies.
   </para>

   <para>
    Quoting an identifier also makes it case-sensitive, whereas
    unquoted names are always folded to lower case.  For example, the
    identifiers <literal>FOO</literal>, <literal>foo</literal>, and
    <literal>"foo"</literal> are considered the same by
    <productname>PostgreSQL</productname>, but
    <literal>"Foo"</literal> and <literal>"FOO"</literal> are
    different from these three and each other.  (The folding of
    unquoted names to lower case in <productname>PostgreSQL</productname> is
    incompatible with the SQL standard, which says that unquoted names
    should be folded to upper case.  Thus, <literal>foo</literal>
    should be equivalent to <literal>"FOO"</literal> not
    <literal>"foo"</literal> according to the standard.  If you want
    to write portable applications you are advised to always quote a
    particular name or never quote it.)
   </para>

   <indexterm>
     <primary>Unicode escape</primary>
     <secondary>in identifiers</secondary>
   </indexterm>

   <para>
    A variant of quoted
    identifiers allows including escaped Unicode characters identified
    by their code points.  This variant starts
    with <literal>U&amp;</literal> (upper or lower case U followed by
    ampersand) immediately before the opening double quote, without
    any spaces in between, for example <literal>U&amp;"foo"</literal>.
    (Note that this creates an ambiguity with the
    operator <literal>&amp;</literal>.  Use spaces around the operator to
    avoid this problem.)  Inside the quotes, Unicode characters can be
    specified in escaped form by writing a backslash followed by the
    four-digit hexadecimal code point number or alternatively a
    backslash followed by a plus sign followed by a six-digit
    hexadecimal code point number.  For example, the
    identifier <literal>"data"</literal> could be written as
<programlisting>
U&amp;"d\0061t\+000061"
</programlisting>
    The following less trivial example writes the Russian
    word <quote>slon</quote> (elephant) in Cyrillic letters:
<programlisting>
U&amp;"\0441\043B\043E\043D"
</programlisting>
   </para>

   <para>
    If a different escape character than backslash is desired, it can
    be specified using
    the <literal>UESCAPE</literal><indexterm><primary>UESCAPE</primary></indexterm>
    clause after the string, for example:
<programlisting>
U&amp;"d!0061t!+000061" UESCAPE '!'
</programlisting>
    The escape character can be any single character other than a
    hexadecimal digit, the plus sign, a single quote, a double quote,
    or a whitespace character.  Note that the escape character is