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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SQL-SYNTAX-LEXICAL"
>4.1. Lexical Structure</A
></H1
><P
> SQL input consists of a sequence of
<I
CLASS="FIRSTTERM"
>commands</I
>. A command is composed of a
sequence of <I
CLASS="FIRSTTERM"
>tokens</I
>, terminated by a
semicolon (<SPAN
CLASS="QUOTE"
>";"</SPAN
>). The end of the input stream also
terminates a command. Which tokens are valid depends on the syntax
of the particular command.
</P
><P
> A token can be a <I
CLASS="FIRSTTERM"
>key word</I
>, an
<I
CLASS="FIRSTTERM"
>identifier</I
>, a <I
CLASS="FIRSTTERM"
>quoted
identifier</I
>, a <I
CLASS="FIRSTTERM"
>literal</I
> (or
constant), or a special character symbol. Tokens are normally
separated by whitespace (space, tab, newline), but need not be if
there is no ambiguity (which is generally only the case if a
special character is adjacent to some other token type).
</P
><P
> For example, the following is (syntactically) valid SQL input:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM MY_TABLE;
UPDATE MY_TABLE SET A = 5;
INSERT INTO MY_TABLE VALUES (3, 'hi there');</PRE
><P>
This is a sequence of three commands, one per line (although this
is not required; more than one command can be on a line, and
commands can usefully be split across lines).
</P
><P
> Additionally, <I
CLASS="FIRSTTERM"
>comments</I
> can occur in SQL
input. They are not tokens, they are effectively equivalent to
whitespace.
</P
><P
> The SQL syntax is not very consistent regarding what tokens
identify commands and which are operands or parameters. The first
few tokens are generally the command name, so in the above example
we would usually speak of a <SPAN
CLASS="QUOTE"
>"SELECT"</SPAN
>, an
<SPAN
CLASS="QUOTE"
>"UPDATE"</SPAN
>, and an <SPAN
CLASS="QUOTE"
>"INSERT"</SPAN
> command. But
for instance the <TT
CLASS="COMMAND"
>UPDATE</TT
> command always requires
a <TT
CLASS="TOKEN"
>SET</TT
> token to appear in a certain position, and
this particular variation of <TT
CLASS="COMMAND"
>INSERT</TT
> also
requires a <TT
CLASS="TOKEN"
>VALUES</TT
> in order to be complete. The
precise syntax rules for each command are described in <A
HREF="reference.html"
>Part VI</A
>.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-IDENTIFIERS"
>4.1.1. Identifiers and Key Words</A
></H2
><P
> Tokens such as <TT
CLASS="TOKEN"
>SELECT</TT
>, <TT
CLASS="TOKEN"
>UPDATE</TT
>, or
<TT
CLASS="TOKEN"
>VALUES</TT
> in the example above are examples of
<I
CLASS="FIRSTTERM"
>key words</I
>, that is, words that have a fixed
meaning in the SQL language. The tokens <TT
CLASS="TOKEN"
>MY_TABLE</TT
>
and <TT
CLASS="TOKEN"
>A</TT
> are examples of
<I
CLASS="FIRSTTERM"
>identifiers</I
>. They identify names of
tables, columns, or other database objects, depending on the
command they are used in. Therefore they are sometimes simply
called <SPAN
CLASS="QUOTE"
>"names"</SPAN
>. Key words and identifiers have the
same lexical structure, meaning that one cannot know whether a
token is an identifier or a key word without knowing the language.
A complete list of key words can be found in <A
HREF="sql-keywords-appendix.html"
>Appendix C</A
>.
</P
><P
> SQL identifiers and key words must begin with a letter
(<TT
CLASS="LITERAL"
>a</TT
>-<TT
CLASS="LITERAL"
>z</TT
>, but also letters with
diacritical marks and non-Latin letters) or an underscore
(<TT
CLASS="LITERAL"
>_</TT
>). Subsequent characters in an identifier or
key word can be letters, underscores, digits
(<TT
CLASS="LITERAL"
>0</TT
>-<TT
CLASS="LITERAL"
>9</TT
>), or dollar signs
(<TT
CLASS="LITERAL"
>$</TT
>). Note that dollar signs are not allowed in identifiers
according to the letter of the SQL standard, so their use might render
applications less portable.
The SQL standard will not define a key word that contains
digits or starts or ends with an underscore, so identifiers of this
form are safe against possible conflict with future extensions of the
standard.
</P
><P
>
The system uses no more than <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
>-1
bytes of an identifier; longer names can be written in
commands, but they will be truncated. By default,
<TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
> is 64 so the maximum identifier
length is 63 bytes. If this limit is problematic, it can be raised by
changing the <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
> constant in
<TT
CLASS="FILENAME"
>src/include/pg_config_manual.h</TT
>.
</P
><P
>
Key words and unquoted identifiers are case insensitive. Therefore:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE MY_TABLE SET A = 5;</PRE
><P>
can equivalently be written as:
</P><PRE
CLASS="PROGRAMLISTING"
>uPDaTE my_TabLE SeT a = 5;</PRE
><P>
A convention often used is to write key words in upper
case and names in lower case, e.g.:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE my_table SET a = 5;</PRE
><P>
</P
><P
>
There is a second kind of identifier: the <I
CLASS="FIRSTTERM"
>delimited
identifier</I
> or <I
CLASS="FIRSTTERM"
>quoted
identifier</I
>. It is formed by enclosing an arbitrary
sequence of characters in double-quotes
(<TT
CLASS="LITERAL"
>"</TT
>). A delimited
identifier is always an identifier, never a key word. So
<TT
CLASS="LITERAL"
>"select"</TT
> could be used to refer to a column or
table named <SPAN
CLASS="QUOTE"
>"select"</SPAN
>, whereas an unquoted
<TT
CLASS="LITERAL"
>select</TT
> 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:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE "my_table" SET "a" = 5;</PRE
><P>
</P
><P
> 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.
</P
><P
> A variant of quoted
identifiers allows including escaped Unicode characters identified
by their code points. This variant starts
with <TT
CLASS="LITERAL"
>U&</TT
> (upper or lower case U followed by
ampersand) immediately before the opening double quote, without
any spaces in between, for example <TT
CLASS="LITERAL"
>U&"foo"</TT
>.
(Note that this creates an ambiguity with the
operator <TT
CLASS="LITERAL"
>&</TT
>. 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 <TT
CLASS="LITERAL"
>"data"</TT
> could be written as
</P><PRE
CLASS="PROGRAMLISTING"
>U&"d\0061t\+000061"</PRE
><P>
The following less trivial example writes the Russian
word <SPAN
CLASS="QUOTE"
>"slon"</SPAN
> (elephant) in Cyrillic letters:
</P><PRE
CLASS="PROGRAMLISTING"
>U&"\0441\043B\043E\043D"</PRE
><P>
</P
><P
> If a different escape character than backslash is desired, it can
be specified using
the <TT
CLASS="LITERAL"
>UESCAPE</TT
>
clause after the string, for example:
</P><PRE
CLASS="PROGRAMLISTING"
>U&"d!0061t!+000061" UESCAPE '!'</PRE
><P>
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
written in single quotes, not double quotes.
</P
><P
> To include the escape character in the identifier literally, write
it twice.
</P
><P
> The Unicode escape syntax works only when the server encoding is
<TT
CLASS="LITERAL"
>UTF8</TT
>. When other server encodings are used, only code
points in the ASCII range (up to <TT
CLASS="LITERAL"
>\007F</TT
>) can be
specified. Both the 4-digit and the 6-digit form can be used to
specify UTF-16 surrogate pairs to compose characters with code
points larger than U+FFFF, although the availability of the
6-digit form technically makes this unnecessary. (Surrogate
pairs are not stored directly, but combined into a single
code point that is then encoded in UTF-8.)
</P
><P
> Quoting an identifier also makes it case-sensitive, whereas
unquoted names are always folded to lower case. For example, the
identifiers <TT
CLASS="LITERAL"
>FOO</TT
>, <TT
CLASS="LITERAL"
>foo</TT
>, and
<TT
CLASS="LITERAL"
>"foo"</TT
> are considered the same by
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, but
<TT
CLASS="LITERAL"
>"Foo"</TT
> and <TT
CLASS="LITERAL"
>"FOO"</TT
> are
different from these three and each other. (The folding of
unquoted names to lower case in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is
incompatible with the SQL standard, which says that unquoted names
should be folded to upper case. Thus, <TT
CLASS="LITERAL"
>foo</TT
>
should be equivalent to <TT
CLASS="LITERAL"
>"FOO"</TT
> not
<TT
CLASS="LITERAL"
>"foo"</TT
> according to the standard. If you want
to write portable applications you are advised to always quote a
particular name or never quote it.)
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-CONSTANTS"
>4.1.2. Constants</A
></H2
><P
> There are three kinds of <I
CLASS="FIRSTTERM"
>implicitly-typed
constants</I
> in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>:
strings, bit strings, and numbers.
Constants can also be specified with explicit types, which can
enable more accurate representation and more efficient handling by
the system. These alternatives are discussed in the following
subsections.
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS"
>4.1.2.1. String Constants</A
></H3
><P
>
A string constant in SQL is an arbitrary sequence of characters
bounded by single quotes (<TT
CLASS="LITERAL"
>'</TT
>), for example
<TT
CLASS="LITERAL"
>'This is a string'</TT
>. To include
a single-quote character within a string constant,
write two adjacent single quotes, e.g.,
<TT
CLASS="LITERAL"
>'Dianne''s horse'</TT
>.
Note that this is <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> the same as a double-quote
character (<TT
CLASS="LITERAL"
>"</TT
>).
</P
><P
> Two string constants that are only separated by whitespace
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>with at least one newline</I
></SPAN
> are concatenated
and effectively treated as if the string had been written as one
constant. For example:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foo'
'bar';</PRE
><P>
is equivalent to:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foobar';</PRE
><P>
but:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foo' 'bar';</PRE
><P>
is not valid syntax. (This slightly bizarre behavior is specified
by <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>; <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is
following the standard.)
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS-ESCAPE"
>4.1.2.2. String Constants with C-style Escapes</A
></H3
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also accepts <SPAN
CLASS="QUOTE"
>"escape"</SPAN
>
string constants, which are an extension to the SQL standard.
An escape string constant is specified by writing the letter
<TT
CLASS="LITERAL"
>E</TT
> (upper or lower case) just before the opening single
quote, e.g., <TT
CLASS="LITERAL"
>E'foo'</TT
>. (When continuing an escape string
constant across lines, write <TT
CLASS="LITERAL"
>E</TT
> only before the first opening
quote.)
Within an escape string, a backslash character (<TT
CLASS="LITERAL"
>\</TT
>) begins a
C-like <I
CLASS="FIRSTTERM"
>backslash escape</I
> sequence, in which the combination
of backslash and following character(s) represent a special byte
value, as shown in <A
HREF="sql-syntax-lexical.html#SQL-BACKSLASH-TABLE"
>Table 4-1</A
>.
</P
><DIV
CLASS="TABLE"
><A
NAME="SQL-BACKSLASH-TABLE"
></A
><P
><B
>Table 4-1. Backslash Escape Sequences</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><THEAD
><TR
><TH
>Backslash Escape Sequence</TH
><TH
>Interpretation</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>\b</TT
></TD
><TD
>backspace</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\f</TT
></TD
><TD
>form feed</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\n</TT
></TD
><TD
>newline</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\r</TT
></TD
><TD
>carriage return</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\t</TT
></TD
><TD
>tab</TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>o</I
></TT
></TT
>,
<TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>oo</I
></TT
></TT
>,
<TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>ooo</I
></TT
></TT
>
(<TT
CLASS="REPLACEABLE"
><I
>o</I
></TT
> = 0 - 7)
</TD
><TD
>octal byte value</TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>\x<TT
CLASS="REPLACEABLE"
><I
>h</I
></TT
></TT
>,
<TT
CLASS="LITERAL"
>\x<TT
CLASS="REPLACEABLE"
><I
>hh</I
></TT
></TT
>
(<TT
CLASS="REPLACEABLE"
><I
>h</I
></TT
> = 0 - 9, A - F)
</TD
><TD
>hexadecimal byte value</TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>\u<TT
CLASS="REPLACEABLE"
><I
>xxxx</I
></TT
></TT
>,
<TT
CLASS="LITERAL"
>\U<TT
CLASS="REPLACEABLE"
><I
>xxxxxxxx</I
></TT
></TT
>
(<TT
CLASS="REPLACEABLE"
><I
>x</I
></TT
> = 0 - 9, A - F)
</TD
><TD
>16 or 32-bit hexadecimal Unicode character value</TD
></TR
></TBODY
></TABLE
></DIV
><P
> Any other
character following a backslash is taken literally. Thus, to
include a backslash character, write two backslashes (<TT
CLASS="LITERAL"
>\\</TT
>).
Also, a single quote can be included in an escape string by writing
<TT
CLASS="LITERAL"
>\'</TT
>, in addition to the normal way of <TT
CLASS="LITERAL"
>''</TT
>.
</P
><P
> It is your responsibility that the byte sequences you create,
especially when using the octal or hexadecimal escapes, compose
valid characters in the server character set encoding. When the
server encoding is UTF-8, then the Unicode escapes or the
alternative Unicode escape syntax, explained
in <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS-UESCAPE"
>Section 4.1.2.3</A
>, should be used
instead. (The alternative would be doing the UTF-8 encoding by
hand and writing out the bytes, which would be very cumbersome.)
</P
><P
> The Unicode escape syntax works fully only when the server
encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>. When other server encodings are
used, only code points in the ASCII range (up
to <TT
CLASS="LITERAL"
>\u007F</TT
>) can be specified. Both the 4-digit and
the 8-digit form can be used to specify UTF-16 surrogate pairs to
compose characters with code points larger than U+FFFF, although
the availability of the 8-digit form technically makes this
unnecessary. (When surrogate pairs are used when the server
encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>, they are first combined into a
single code point that is then encoded in UTF-8.)
</P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> If the configuration parameter
<A
HREF="runtime-config-compatible.html#GUC-STANDARD-CONFORMING-STRINGS"
>standard_conforming_strings</A
> is <TT
CLASS="LITERAL"
>off</TT
>,
then <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> recognizes backslash escapes
in both regular and escape string constants. However, as of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.1, the default is <TT
CLASS="LITERAL"
>on</TT
>, meaning
that backslash escapes are recognized only in escape string constants.
This behavior is more standards-compliant, but might break applications
which rely on the historical behavior, where backslash escapes
were always recognized. As a workaround, you can set this parameter
to <TT
CLASS="LITERAL"
>off</TT
>, but it is better to migrate away from using backslash
escapes. If you need to use a backslash escape to represent a special
character, write the string constant with an <TT
CLASS="LITERAL"
>E</TT
>.
</P
><P
> In addition to <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
>, the configuration
parameters <A
HREF="runtime-config-compatible.html#GUC-ESCAPE-STRING-WARNING"
>escape_string_warning</A
> and
<A
HREF="runtime-config-compatible.html#GUC-BACKSLASH-QUOTE"
>backslash_quote</A
> govern treatment of backslashes
in string constants.
</P
></TD
></TR
></TABLE
></DIV
><P
> The character with the code zero cannot be in a string constant.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS-UESCAPE"
>4.1.2.3. String Constants with Unicode Escapes</A
></H3
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also supports another type
of escape syntax for strings that allows specifying arbitrary
Unicode characters by code point. A Unicode escape string
constant starts with <TT
CLASS="LITERAL"
>U&</TT
> (upper or lower case
letter U followed by ampersand) immediately before the opening
quote, without any spaces in between, for
example <TT
CLASS="LITERAL"
>U&'foo'</TT
>. (Note that this creates an
ambiguity with the operator <TT
CLASS="LITERAL"
>&</TT
>. 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 string <TT
CLASS="LITERAL"
>'data'</TT
> could be written as
</P><PRE
CLASS="PROGRAMLISTING"
>U&'d\0061t\+000061'</PRE
><P>
The following less trivial example writes the Russian
word <SPAN
CLASS="QUOTE"
>"slon"</SPAN
> (elephant) in Cyrillic letters:
</P><PRE
CLASS="PROGRAMLISTING"
>U&'\0441\043B\043E\043D'</PRE
><P>
</P
><P
> If a different escape character than backslash is desired, it can
be specified using
the <TT
CLASS="LITERAL"
>UESCAPE</TT
>
clause after the string, for example:
</P><PRE
CLASS="PROGRAMLISTING"
>U&'d!0061t!+000061' UESCAPE '!'</PRE
><P>
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.
</P
><P
> The Unicode escape syntax works only when the server encoding is
<TT
CLASS="LITERAL"
>UTF8</TT
>. When other server encodings are used, only
code points in the ASCII range (up to <TT
CLASS="LITERAL"
>\007F</TT
>)
can be specified. Both the 4-digit and the 6-digit form can be
used to specify UTF-16 surrogate pairs to compose characters with
code points larger than U+FFFF, although the availability of the
6-digit form technically makes this unnecessary. (When surrogate
pairs are used when the server encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>, they
are first combined into a single code point that is then encoded
in UTF-8.)
</P
><P
> Also, the Unicode escape syntax for string constants only works
when the configuration
parameter <A
HREF="runtime-config-compatible.html#GUC-STANDARD-CONFORMING-STRINGS"
>standard_conforming_strings</A
> is
turned on. This is because otherwise this syntax could confuse
clients that parse the SQL statements to the point that it could
lead to SQL injections and similar security issues. If the
parameter is set to off, this syntax will be rejected with an
error message.
</P
><P
> To include the escape character in the string literally, write it
twice.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-DOLLAR-QUOTING"
>4.1.2.4. Dollar-quoted String Constants</A
></H3
><P
> While the standard syntax for specifying string constants is usually
convenient, it can be difficult to understand when the desired string
contains many single quotes or backslashes, since each of those must
be doubled. To allow more readable queries in such situations,
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides another way, called
<SPAN
CLASS="QUOTE"
>"dollar quoting"</SPAN
>, to write string constants.
A dollar-quoted string constant
consists of a dollar sign (<TT
CLASS="LITERAL"
>$</TT
>), an optional
<SPAN
CLASS="QUOTE"
>"tag"</SPAN
> of zero or more characters, another dollar
sign, an arbitrary sequence of characters that makes up the
string content, a dollar sign, the same tag that began this
dollar quote, and a dollar sign. For example, here are two
different ways to specify the string <SPAN
CLASS="QUOTE"
>"Dianne's horse"</SPAN
>
using dollar quoting:
</P><PRE
CLASS="PROGRAMLISTING"
>$$Dianne's horse$$
$SomeTag$Dianne's horse$SomeTag$</PRE
><P>
Notice that inside the dollar-quoted string, single quotes can be
used without needing to be escaped. Indeed, no characters inside
a dollar-quoted string are ever escaped: the string content is always
written literally. Backslashes are not special, and neither are
dollar signs, unless they are part of a sequence matching the opening
tag.
</P
><P
> It is possible to nest dollar-quoted string constants by choosing
different tags at each nesting level. This is most commonly used in
writing function definitions. For example:
</P><PRE
CLASS="PROGRAMLISTING"
>$function$
BEGIN
RETURN ($1 ~ $q$[\t\r\n\v\\]$q$);
END;
$function$</PRE
><P>
Here, the sequence <TT
CLASS="LITERAL"
>$q$[\t\r\n\v\\]$q$</TT
> represents a
dollar-quoted literal string <TT
CLASS="LITERAL"
>[\t\r\n\v\\]</TT
>, which will
be recognized when the function body is executed by
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>. But since the sequence does not match
the outer dollar quoting delimiter <TT
CLASS="LITERAL"
>$function$</TT
>, it is
just some more characters within the constant so far as the outer
string is concerned.
</P
><P
> The tag, if any, of a dollar-quoted string follows the same rules
as an unquoted identifier, except that it cannot contain a dollar sign.
Tags are case sensitive, so <TT
CLASS="LITERAL"
>$tag$String content$tag$</TT
>
is correct, but <TT
CLASS="LITERAL"
>$TAG$String content$tag$</TT
> is not.
</P
><P
> A dollar-quoted string that follows a keyword or identifier must
be separated from it by whitespace; otherwise the dollar quoting
delimiter would be taken as part of the preceding identifier.
</P
><P
> Dollar quoting is not part of the SQL standard, but it is often a more
convenient way to write complicated string literals than the
standard-compliant single quote syntax. It is particularly useful when
representing string constants inside other constants, as is often needed
in procedural function definitions. With single-quote syntax, each
backslash in the above example would have to be written as four
backslashes, which would be reduced to two backslashes in parsing the
original string constant, and then to one when the inner string constant
is re-parsed during function execution.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-BIT-STRINGS"
>4.1.2.5. Bit-string Constants</A
></H3
><P
> Bit-string constants look like regular string constants with a
<TT
CLASS="LITERAL"
>B</TT
> (upper or lower case) immediately before the
opening quote (no intervening whitespace), e.g.,
<TT
CLASS="LITERAL"
>B'1001'</TT
>. The only characters allowed within
bit-string constants are <TT
CLASS="LITERAL"
>0</TT
> and
<TT
CLASS="LITERAL"
>1</TT
>.
</P
><P
> Alternatively, bit-string constants can be specified in hexadecimal
notation, using a leading <TT
CLASS="LITERAL"
>X</TT
> (upper or lower case),
e.g., <TT
CLASS="LITERAL"
>X'1FF'</TT
>. This notation is equivalent to
a bit-string constant with four binary digits for each hexadecimal digit.
</P
><P
> Both forms of bit-string constant can be continued
across lines in the same way as regular string constants.
Dollar quoting cannot be used in a bit-string constant.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-CONSTANTS-NUMERIC"
>4.1.2.6. Numeric Constants</A
></H3
><P
> Numeric constants are accepted in these general forms:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>
<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>.[<SPAN
CLASS="OPTIONAL"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>][<SPAN
CLASS="OPTIONAL"
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>]
[<SPAN
CLASS="OPTIONAL"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>].<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>[<SPAN
CLASS="OPTIONAL"
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>]
<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></PRE
><P>
where <TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
> is one or more decimal
digits (0 through 9). At least one digit must be before or after the
decimal point, if one is used. At least one digit must follow the
exponent marker (<TT
CLASS="LITERAL"
>e</TT
>), if one is present.
There cannot be any spaces or other characters embedded in the
constant. Note that any leading plus or minus sign is not actually
considered part of the constant; it is an operator applied to the
constant.
</P
><P
> These are some examples of valid numeric constants:
<P
CLASS="LITERALLAYOUT"
>42<br>
3.5<br>
4.<br>
.001<br>
5e2<br>
1.925e-3</P
>
</P
><P
>
A numeric constant that contains neither a decimal point nor an
exponent is initially presumed to be type <TT
CLASS="TYPE"
>integer</TT
> if its
value fits in type <TT
CLASS="TYPE"
>integer</TT
> (32 bits); otherwise it is
presumed to be type <TT
CLASS="TYPE"
>bigint</TT
> if its
value fits in type <TT
CLASS="TYPE"
>bigint</TT
> (64 bits); otherwise it is
taken to be type <TT
CLASS="TYPE"
>numeric</TT
>. Constants that contain decimal
points and/or exponents are always initially presumed to be type
<TT
CLASS="TYPE"
>numeric</TT
>.
</P
><P
> The initially assigned data type of a numeric constant is just a
starting point for the type resolution algorithms. In most cases
the constant will be automatically coerced to the most
appropriate type depending on context. When necessary, you can
force a numeric value to be interpreted as a specific data type
by casting it.
For example, you can force a numeric value to be treated as type
<TT
CLASS="TYPE"
>real</TT
> (<TT
CLASS="TYPE"
>float4</TT
>) by writing:
</P><PRE
CLASS="PROGRAMLISTING"
>REAL '1.23' -- string style
1.23::REAL -- PostgreSQL (historical) style</PRE
><P>
These are actually just special cases of the general casting
notations discussed next.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-CONSTANTS-GENERIC"
>4.1.2.7. Constants of Other Types</A
></H3
><P
> A constant of an <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>arbitrary</I
></SPAN
> type can be
entered using any one of the following notations:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'
'<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'::<TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
>
CAST ( '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>' AS <TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> )</PRE
><P>
The string constant's text is passed to the input conversion
routine for the type called <TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
>. The
result is a constant of the indicated type. The explicit type
cast can be omitted if there is no ambiguity as to the type the
constant must be (for example, when it is assigned directly to a
table column), in which case it is automatically coerced.
</P
><P
> The string constant can be written using either regular SQL
notation or dollar-quoting.
</P
><P
> It is also possible to specify a type coercion using a function-like
syntax:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>typename</I
></TT
> ( '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>' )</PRE
><P>
but not all type names can be used in this way; see <A
HREF="sql-expressions.html#SQL-SYNTAX-TYPE-CASTS"
>Section 4.2.9</A
> for details.
</P
><P
> The <TT
CLASS="LITERAL"
>::</TT
>, <TT
CLASS="LITERAL"
>CAST()</TT
>, and
function-call syntaxes can also be used to specify run-time type
conversions of arbitrary expressions, as discussed in <A
HREF="sql-expressions.html#SQL-SYNTAX-TYPE-CASTS"
>Section 4.2.9</A
>. To avoid syntactic ambiguity, the
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
syntax can only be used to specify the type of a simple literal constant.
Another restriction on the
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
syntax is that it does not work for array types; use <TT
CLASS="LITERAL"
>::</TT
>
or <TT
CLASS="LITERAL"
>CAST()</TT
> to specify the type of an array constant.
</P
><P
> The <TT
CLASS="LITERAL"
>CAST()</TT
> syntax conforms to SQL. The
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
syntax is a generalization of the standard: SQL specifies this syntax only
for a few data types, but <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allows it
for all types. The syntax with
<TT
CLASS="LITERAL"
>::</TT
> is historical <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
usage, as is the function-call syntax.
</P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-OPERATORS"
>4.1.3. Operators</A
></H2
><P
> An operator name is a sequence of up to <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
>-1
(63 by default) characters from the following list:
<P
CLASS="LITERALLAYOUT"
>+ - * / < > = ~ ! @ # % ^ & | ` ?</P
>
There are a few restrictions on operator names, however:
<P
></P
></P><UL
><LI
><P
> <TT
CLASS="LITERAL"
>--</TT
> and <TT
CLASS="LITERAL"
>/*</TT
> cannot appear
anywhere in an operator name, since they will be taken as the
start of a comment.
</P
></LI
><LI
><P
> A multiple-character operator name cannot end in <TT
CLASS="LITERAL"
>+</TT
> or <TT
CLASS="LITERAL"
>-</TT
>,
unless the name also contains at least one of these characters:
<P
CLASS="LITERALLAYOUT"
>~ ! @ # % ^ & | ` ?</P
>
For example, <TT
CLASS="LITERAL"
>@-</TT
> is an allowed operator name,
but <TT
CLASS="LITERAL"
>*-</TT
> is not. This restriction allows
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> to parse SQL-compliant
queries without requiring spaces between tokens.
</P
></LI
></UL
><P>
</P
><P
> When working with non-SQL-standard operator names, you will usually
need to separate adjacent operators with spaces to avoid ambiguity.
For example, if you have defined a left unary operator named <TT
CLASS="LITERAL"
>@</TT
>,
you cannot write <TT
CLASS="LITERAL"
>X*@Y</TT
>; you must write
<TT
CLASS="LITERAL"
>X* @Y</TT
> to ensure that
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> reads it as two operator names
not one.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-SPECIAL-CHARS"
>4.1.4. Special Characters</A
></H2
><P
> Some characters that are not alphanumeric have a special meaning
that is different from being an operator. Details on the usage can
be found at the location where the respective syntax element is
described. This section only exists to advise the existence and
summarize the purposes of these characters.
<P
></P
></P><UL
><LI
><P
> A dollar sign (<TT
CLASS="LITERAL"
>$</TT
>) followed by digits is used
to represent a positional parameter in the body of a function
definition or a prepared statement. In other contexts the
dollar sign can be part of an identifier or a dollar-quoted string
constant.
</P
></LI
><LI
><P
> Parentheses (<TT
CLASS="LITERAL"
>()</TT
>) have their usual meaning to
group expressions and enforce precedence. In some cases
parentheses are required as part of the fixed syntax of a
particular SQL command.
</P
></LI
><LI
><P
> Brackets (<TT
CLASS="LITERAL"
>[]</TT
>) are used to select the elements
of an array. See <A
HREF="arrays.html"
>Section 8.15</A
> for more information
on arrays.
</P
></LI
><LI
><P
> Commas (<TT
CLASS="LITERAL"
>,</TT
>) are used in some syntactical
constructs to separate the elements of a list.
</P
></LI
><LI
><P
> The semicolon (<TT
CLASS="LITERAL"
>;</TT
>) terminates an SQL command.
It cannot appear anywhere within a command, except within a
string constant or quoted identifier.
</P
></LI
><LI
><P
> The colon (<TT
CLASS="LITERAL"
>:</TT
>) is used to select
<SPAN
CLASS="QUOTE"
>"slices"</SPAN
> from arrays. (See <A
HREF="arrays.html"
>Section 8.15</A
>.) In certain SQL dialects (such as Embedded
SQL), the colon is used to prefix variable names.
</P
></LI
><LI
><P
> The asterisk (<TT
CLASS="LITERAL"
>*</TT
>) is used in some contexts to denote
all the fields of a table row or composite value. It also
has a special meaning when used as the argument of an
aggregate function, namely that the aggregate does not require
any explicit parameter.
</P
></LI
><LI
><P
> The period (<TT
CLASS="LITERAL"
>.</TT
>) is used in numeric
constants, and to separate schema, table, and column names.
</P
></LI
></UL
><P>
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-COMMENTS"
>4.1.5. Comments</A
></H2
><P
> A comment is a sequence of characters beginning with
double dashes and extending to the end of the line, e.g.:
</P><PRE
CLASS="PROGRAMLISTING"
>-- This is a standard SQL comment</PRE
><P>
</P
><P
> Alternatively, C-style block comments can be used:
</P><PRE
CLASS="PROGRAMLISTING"
>/* multiline comment
* with nesting: /* nested block comment */
*/</PRE
><P>
where the comment begins with <TT
CLASS="LITERAL"
>/*</TT
> and extends to
the matching occurrence of <TT
CLASS="LITERAL"
>*/</TT
>. These block
comments nest, as specified in the SQL standard but unlike C, so that one can
comment out larger blocks of code that might contain existing block
comments.
</P
><P
> A comment is removed from the input stream before further syntax
analysis and is effectively replaced by whitespace.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-PRECEDENCE"
>4.1.6. Operator Precedence</A
></H2
><P
> <A
HREF="sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE"
>Table 4-2</A
> shows the precedence and
associativity of the operators in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.
Most operators have the same precedence and are left-associative.
The precedence and associativity of the operators is hard-wired
into the parser. This can lead to non-intuitive behavior; for
example the Boolean operators <TT
CLASS="LITERAL"
><</TT
> and
<TT
CLASS="LITERAL"
>></TT
> have a different precedence than the Boolean
operators <TT
CLASS="LITERAL"
><=</TT
> and <TT
CLASS="LITERAL"
>>=</TT
>. Also, you will
sometimes need to add parentheses when using combinations of
binary and unary operators. For instance:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 5 ! - 6;</PRE
><P>
will be parsed as:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 5 ! (- 6);</PRE
><P>
because the parser has no idea — until it is too late
— that <TT
CLASS="TOKEN"
>!</TT
> is defined as a postfix operator,
not an infix one. To get the desired behavior in this case, you
must write:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT (5 !) - 6;</PRE
><P>
This is the price one pays for extensibility.
</P
><DIV
CLASS="TABLE"
><A
NAME="SQL-PRECEDENCE-TABLE"
></A
><P
><B
>Table 4-2. Operator Precedence (decreasing)</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Operator/Element</TH
><TH
>Associativity</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="TOKEN"
>.</TT
></TD
><TD
>left</TD
><TD
>table/column name separator</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>::</TT
></TD
><TD
>left</TD
><TD
><SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>-style typecast</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>[</TT
> <TT
CLASS="TOKEN"
>]</TT
></TD
><TD
>left</TD
><TD
>array element selection</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>+</TT
> <TT
CLASS="TOKEN"
>-</TT
></TD
><TD
>right</TD
><TD
>unary plus, unary minus</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>^</TT
></TD
><TD
>left</TD
><TD
>exponentiation</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>*</TT
> <TT
CLASS="TOKEN"
>/</TT
> <TT
CLASS="TOKEN"
>%</TT
></TD
><TD
>left</TD
><TD
>multiplication, division, modulo</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>+</TT
> <TT
CLASS="TOKEN"
>-</TT
></TD
><TD
>left</TD
><TD
>addition, subtraction</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>IS</TT
></TD
><TD
> </TD
><TD
><TT
CLASS="LITERAL"
>IS TRUE</TT
>, <TT
CLASS="LITERAL"
>IS FALSE</TT
>, <TT
CLASS="LITERAL"
>IS NULL</TT
>, etc</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>ISNULL</TT
></TD
><TD
> </TD
><TD
>test for null</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>NOTNULL</TT
></TD
><TD
> </TD
><TD
>test for not null</TD
></TR
><TR
><TD
>(any other)</TD
><TD
>left</TD
><TD
>all other native and user-defined operators</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>IN</TT
></TD
><TD
> </TD
><TD
>set membership</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>BETWEEN</TT
></TD
><TD
> </TD
><TD
>range containment</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>OVERLAPS</TT
></TD
><TD
> </TD
><TD
>time interval overlap</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>LIKE</TT
> <TT
CLASS="TOKEN"
>ILIKE</TT
> <TT
CLASS="TOKEN"
>SIMILAR</TT
></TD
><TD
> </TD
><TD
>string pattern matching</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
><</TT
> <TT
CLASS="TOKEN"
>></TT
></TD
><TD
> </TD
><TD
>less than, greater than</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>=</TT
></TD
><TD
>right</TD
><TD
>equality, assignment</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>NOT</TT
></TD
><TD
>right</TD
><TD
>logical negation</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>AND</TT
></TD
><TD
>left</TD
><TD
>logical conjunction</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>OR</TT
></TD
><TD
>left</TD
><TD
>logical disjunction</TD
></TR
></TBODY
></TABLE
></DIV
><P
> Note that the operator precedence rules also apply to user-defined
operators that have the same names as the built-in operators
mentioned above. For example, if you define a
<SPAN
CLASS="QUOTE"
>"+"</SPAN
> operator for some custom data type it will have
the same precedence as the built-in <SPAN
CLASS="QUOTE"
>"+"</SPAN
> operator, no
matter what yours does.
</P
><P
> When a schema-qualified operator name is used in the
<TT
CLASS="LITERAL"
>OPERATOR</TT
> syntax, as for example in:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 3 OPERATOR(pg_catalog.+) 4;</PRE
><P>
the <TT
CLASS="LITERAL"
>OPERATOR</TT
> construct is taken to have the default precedence
shown in <A
HREF="sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE"
>Table 4-2</A
> for <SPAN
CLASS="QUOTE"
>"any other"</SPAN
> operator. This is true no matter
which specific operator appears inside <TT
CLASS="LITERAL"
>OPERATOR()</TT
>.
</P
></DIV
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