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Fix example of syntactic ambiguity between prefix/infix/postfix operators

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--- Postgres now accepts the example we claimed it wouldn't.  Miscellaneous
copy-editing as well.
This commit is contained in:
Tom Lane 2001-02-10 07:08:44 +00:00
parent 755a87332a
commit 08265ef9c2
1 changed files with 38 additions and 29 deletions
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doc/src/sgml/syntax.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.38 2001/01/26 22:04:22 petere Exp $ $Header: /cvsroot/pgsql/doc/src/sgml/syntax.sgml,v 1.39 2001/02/10 07:08:44 tgl Exp $
--> -->
<chapter id="sql-syntax"> <chapter id="sql-syntax">
@ -49,7 +49,7 @@ INSERT INTO MY_TABLE VALUES (3, 'hi there');
</programlisting> </programlisting>
This is a sequence of three commands, one per line (although this 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 is not required; more than one command can be on a line, and
commands can be usefully split across lines). commands can usefully be split across lines).
</para> </para>
</informalexample> </informalexample>
@ -115,7 +115,7 @@ UPDATE MY_TABLE SET A = 5;
<programlisting> <programlisting>
uPDaTE my_TabLE SeT a = 5; uPDaTE my_TabLE SeT a = 5;
</programlisting> </programlisting>
A good convention to adopt is perhaps to write key words in upper A convention often used is to write key words in upper
case and names in lower case, e.g., case and names in lower case, e.g.,
<programlisting> <programlisting>
UPDATE my_table SET a = 5; UPDATE my_table SET a = 5;
@ -131,10 +131,10 @@ UPDATE my_table SET a = 5;
identifier is always an identifier, never a key word. So identifier is always an identifier, never a key word. So
<literal>"select"</literal> could be used to refer to a column or <literal>"select"</literal> could be used to refer to a column or
table named <quote>select</quote>, whereas an unquoted table named <quote>select</quote>, whereas an unquoted
<literal>select</literal> would be taken as part of a command and <literal>select</literal> would be taken as a key word and
would therefore provoke a parse error when used where a table or would therefore provoke a parse error when used where a table or
column name is expected. The example can be written with quoted column name is expected. The example can be written with quoted
identifiers like so: identifiers like this:
<programlisting> <programlisting>
UPDATE "my_table" SET "a" = 5; UPDATE "my_table" SET "a" = 5;
</programlisting> </programlisting>
@ -157,11 +157,13 @@ UPDATE "my_table" SET "a" = 5;
each other. each other.
<footnote> <footnote>
<para> <para>
This is incompatible with SQL, where unquoted names are folded to <productname>Postgres</productname>' folding of unquoted names to lower
upper case. Thus, <literal>foo</literal> is equivalent to case is incompatible with the SQL standard, which says that unquoted
<literal>"FOO"</literal>. If you want to write portable names should be folded to upper case. Thus, <literal>foo</literal>
applications you are advised to always quote a particular name or should be equivalent to <literal>"FOO"</literal> not
never quote it. <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> </para>
</footnote> </footnote>
</para> </para>
@ -241,7 +243,7 @@ SELECT 'foo' 'bar';
opening quote (no intervening whitespace), e.g., opening quote (no intervening whitespace), e.g.,
<literal>B'1001'</literal>. The only characters allowed within <literal>B'1001'</literal>. The only characters allowed within
bit string constants are <literal>0</literal> and bit string constants are <literal>0</literal> and
<literal>1</literal>. Bit strings constants can be continued <literal>1</literal>. Bit string constants can be continued
across lines in the same way as regular string constants. across lines in the same way as regular string constants.
</para> </para>
</sect3> </sect3>
@ -271,7 +273,7 @@ SELECT 'foo' 'bar';
</synopsis> </synopsis>
where <replaceable>digits</replaceable> is one or more decimal where <replaceable>digits</replaceable> is one or more decimal
digits. At least one digit must be before or after the decimal digits. At least one digit must be before or after the decimal
point and after the <literal>e</literal> if you use that option. point, and after the <literal>e</literal> if you use that option.
Thus, a floating point constant is distinguished from an integer Thus, a floating point constant is distinguished from an integer
constant by the presence of either the decimal point or the constant by the presence of either the decimal point or the
exponent clause (or both). There must not be a space or other exponent clause (or both). There must not be a space or other
@ -486,8 +488,8 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
<listitem> <listitem>
<para> <para>
The semicolon (<literal>;</literal>) terminates an SQL command. The semicolon (<literal>;</literal>) terminates an SQL command.
It cannot appear anywhere within a command, except when quoted It cannot appear anywhere within a command, except within a
as a string constant or identifier. string constant or quoted identifier.
</para> </para>
</listitem> </listitem>
@ -648,7 +650,7 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
<para> <para>
For further information on the system attributes consult For further information on the system attributes consult
<xref linkend="STON87a" endterm="STON87a">. <xref linkend="STON87a" endterm="STON87a">.
Transaction and command identifiers are 32 bit quantities. Transaction and command identifiers are 32-bit quantities.
</para> </para>
</sect1> </sect1>
@ -658,7 +660,7 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
<title>Value Expressions</title> <title>Value Expressions</title>
<para> <para>
Value expressions are used in a variety of syntactic contexts, such Value expressions are used in a variety of contexts, such
as in the target list of the <command>SELECT</command> command, as as in the target list of the <command>SELECT</command> command, as
new column values in <command>INSERT</command> or new column values in <command>INSERT</command> or
<command>UPDATE</command>, or in search conditions in a number of <command>UPDATE</command>, or in search conditions in a number of
@ -692,13 +694,13 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
An operator invocation: An operator invocation:
<simplelist> <simplelist>
<member><replaceable>expression</replaceable> <replaceable>operator</replaceable> <replaceable>expression</replaceable> (binary infix operator)</member> <member><replaceable>expression</replaceable> <replaceable>operator</replaceable> <replaceable>expression</replaceable> (binary infix operator)</member>
<member><replaceable>expression</replaceable> <replaceable>operator</replaceable> (unary postfix operator)</member>
<member><replaceable>operator</replaceable> <replaceable>expression</replaceable> (unary prefix operator)</member> <member><replaceable>operator</replaceable> <replaceable>expression</replaceable> (unary prefix operator)</member>
<member><replaceable>expression</replaceable> <replaceable>operator</replaceable> (unary postfix operator)</member>
</simplelist> </simplelist>
where <replaceable>operator</replaceable> follows the syntax where <replaceable>operator</replaceable> follows the syntax
rules of <xref linkend="sql-syntax-operators"> or is one of the rules of <xref linkend="sql-syntax-operators"> or is one of the
tokens <token>AND</token>, <token>OR</token>, and tokens <token>AND</token>, <token>OR</token>, and
<token>NOT</token>. What particular operators exist and whether <token>NOT</token>. Which particular operators exist and whether
they are unary or binary depends on what operators have been they are unary or binary depends on what operators have been
defined by the system or the user. <xref linkend="functions"> defined by the system or the user. <xref linkend="functions">
describes the built-in operators. describes the built-in operators.
@ -733,7 +735,7 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
<listitem> <listitem>
<para> <para>
A scalar subquery. This is an ordinary A scalar subquery. This is an ordinary
<command>SELECT</command> in parenthesis that returns exactly one <command>SELECT</command> in parentheses that returns exactly one
row with one column. It is an error to use a subquery that row with one column. It is an error to use a subquery that
returns more than one row or more than one column in the context returns more than one row or more than one column in the context
of a value expression. of a value expression.
@ -813,9 +815,9 @@ CREATE FUNCTION dept (text) RETURNS dept
<title>Function Calls</title> <title>Function Calls</title>
<para> <para>
The syntax for a function call is the name of a legal function The syntax for a function call is the name of a function
(subject to the syntax rules for identifiers of <xref (which is subject to the syntax rules for identifiers of <xref
linkend="sql-syntax-identifiers"> , followed by its argument list linkend="sql-syntax-identifiers">), followed by its argument list
enclosed in parentheses: enclosed in parentheses:
<synopsis> <synopsis>
@ -862,7 +864,9 @@ sqrt(2)
<para> <para>
The first form of aggregate expression invokes the aggregate The first form of aggregate expression invokes the aggregate
across all input rows for which the given expression yields a across all input rows for which the given expression yields a
non-NULL value. The second form is the same as the first, since non-NULL value. (Actually, it is up to the aggregate function
whether to ignore NULLs or not --- but all the standard ones do.)
The second form is the same as the first, since
<literal>ALL</literal> is the default. The third form invokes the <literal>ALL</literal> is the default. The third form invokes the
aggregate for all distinct non-NULL values of the expression found aggregate for all distinct non-NULL values of the expression found
in the input rows. The last form invokes the aggregate once for in the input rows. The last form invokes the aggregate once for
@ -881,7 +885,8 @@ sqrt(2)
<para> <para>
The predefined aggregate functions are described in <xref The predefined aggregate functions are described in <xref
linkend="functions-aggregate">. linkend="functions-aggregate">. Other aggregate functions may be added
by the user.
</para> </para>
</sect2> </sect2>
@ -900,15 +905,19 @@ sqrt(2)
you will sometimes need to add parentheses when using combinations you will sometimes need to add parentheses when using combinations
of binary and unary operators. For instance of binary and unary operators. For instance
<programlisting> <programlisting>
SELECT 5 &amp; ~ 6; SELECT 5 ! ~ 6;
</programlisting> </programlisting>
will be parsed as will be parsed as
<programlisting> <programlisting>
SELECT (5 &amp;) ~ 6; SELECT 5 ! (~ 6);
</programlisting> </programlisting>
because the parser has no idea that <token>&amp;</token> is because the parser has no idea --- until it's too late --- that
defined as a binary operator. This is the price one pays for <token>!</token> is defined as a postfix operator not an infix one.
extensibility. To get the desired behavior in this case, you must write
<programlisting>
SELECT (5 !) ~ 6;
</programlisting>
This is the price one pays for extensibility.
</para> </para>
<table tocentry="1"> <table tocentry="1">