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Modify lexing of multi-char operators per pghackers discussion around

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16-Mar-00: trailing + or - is not part of the operator unless the operator
also contains characters not present in SQL92-defined operators.  This
solves the 'X=-Y' problem without unduly constraining users' choice of
operator names --- in particular, no existing Postgres operator names
become invalid.

Also, remove processing of // comments, as agreed in the same thread.
This commit is contained in:
Tom Lane
2000-03-18 18:03:12 +00:00
parent 2b23e86447
commit f945f46193
5 changed files with 211 additions and 81 deletions
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87
doc/src/sgml/ref/create_operator.sgml
View File

@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.11 1999/07/22 15:09:08 thomas Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_operator.sgml,v 1.12 2000/03/18 18:03:12 tgl Exp $
Postgres documentation
-->
@ -60,8 +60,8 @@ CREATE OPERATOR <replaceable>name</replaceable> ( PROCEDURE = <replaceable class
<term><replaceable class="parameter">type1</replaceable></term>
<listitem>
<para>
The type for the left-hand side of the operator, if any. This option would be
omitted for a right-unary operator.
The type of the left-hand argument of the operator, if any.
This option would be omitted for a left-unary operator.
</para>
</listitem>
</varlistentry>
@ -69,8 +69,8 @@ CREATE OPERATOR <replaceable>name</replaceable> ( PROCEDURE = <replaceable class
<term><replaceable class="parameter">type2</replaceable></term>
<listitem>
<para>
The type for the right-hand side of the operator, if any. This option would be
omitted for a left-unary operator.
The type of the right-hand argument of the operator, if any.
This option would be omitted for a right-unary operator.
</para>
</listitem>
</varlistentry>
@ -78,7 +78,7 @@ CREATE OPERATOR <replaceable>name</replaceable> ( PROCEDURE = <replaceable class
<term><replaceable class="parameter">com_op</replaceable></term>
<listitem>
<para>
The commutator for this operator.
The commutator of this operator.
</para>
</listitem>
</varlistentry>
@ -110,7 +110,7 @@ CREATE OPERATOR <replaceable>name</replaceable> ( PROCEDURE = <replaceable class
<term>HASHES</term>
<listitem>
<para>
Indicates this operator can support a hash-join algorithm.
Indicates this operator can support a hash join.
</para>
</listitem>
</varlistentry>
@ -118,7 +118,8 @@ Indicates this operator can support a hash-join algorithm.
<term><replaceable class="parameter">left_sort_op</replaceable></term>
<listitem>
<para>
Operator that sorts the left-hand data type of this operator.
If this operator can support a merge join, the
operator that sorts the left-hand data type of this operator.
</para>
</listitem>
</varlistentry>
@ -126,7 +127,8 @@ Indicates this operator can support a hash-join algorithm.
<term><replaceable class="parameter">right_sort_op</replaceable></term>
<listitem>
<para>
Operator that sorts the right-hand data type of this operator.
If this operator can support a merge join, the
operator that sorts the right-hand data type of this operator.
</para>
</listitem>
</varlistentry>
@ -172,22 +174,56 @@ CREATE
</para>
<para>
The operator <replaceable class="parameter">name</replaceable>
is a sequence of up to thirty two (32) characters in any combination
from the following:
is a sequence of up to NAMEDATALEN-1 (31 by default) characters
from the following list:
<literallayout>
+ - * / &lt; &gt; = ~ ! @ # % ^ & | ` ? $ :
+ - * / &lt; &gt; = ~ ! @ # % ^ &amp; | ` ? $ :
</literallayout>
There are a few restrictions on your choice of name:
<itemizedlist>
<listitem>
<para>
"$" and ":" cannot be defined as single-character operators,
although they can be part of a multi-character operator name.
</para>
</listitem>
<listitem>
<para>
"--" and "/*" cannot appear anywhere in an operator name,
since they will be taken as the start of a comment.
</para>
</listitem>
<listitem>
<para>
A multi-character operator name cannot end in "+" or "-",
unless the name also contains at least one of these characters:
<literallayout>
~ ! @ # % ^ &amp; | ` ? $ :
</literallayout>
For example, <literal>@-</literal> is an allowed operator name,
but <literal>*-</literal> is not.
This restriction allows <productname>Postgres</productname> to
parse SQL-compliant queries without requiring spaces between tokens.
</para>
</listitem>
</itemizedlist>
<note>
<para>
No alphabetic characters are allowed in an operator name.
This enables <productname>Postgres</productname> to parse SQL input
into tokens without requiring spaces between each token.
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 "@",
you cannot write <literal>X*@Y</literal>; you must write
<literal>X* @Y</literal> to ensure that
<productname>Postgres</productname> reads it as two operator names
not one.
</para>
</note>
</para>
<para>
The operator "!=" is mapped to "&lt;&gt;" on input, so they are
therefore equivalent.
The operator "!=" is mapped to "&lt;&gt;" on input, so these two names
are always equivalent.
</para>
<para>
At least one of LEFTARG and RIGHTARG must be defined. For
@ -196,11 +232,11 @@ CREATE
unary operators only RIGHTARG should be defined.
</para>
<para>
Also, the
The
<replaceable class="parameter">func_name</replaceable> procedure must have
been previously defined using <command>CREATE FUNCTION</command> and must
be defined to accept the correct number of arguments
(either one or two).
(either one or two) of the indicated types.
</para>
<para>
The commutator operator should be identified if one exists,
@ -247,8 +283,6 @@ MYBOXES.description !== "0,0,1,1"::box
does not yet have a commutator itself, then the commutator's
entry is updated to have the newly created operator as its
commutator. This applies to the negator, as well.
</para>
<para>
This is to allow the definition of two operators that are
the commutators or the negators of each other. The first
operator should be defined without a commutator or negator
@ -258,7 +292,7 @@ MYBOXES.description !== "0,0,1,1"::box
it also works to just have both operators refer to each other.)
</para>
<para>
The next three specifications are present to support the
The HASHES, SORT1, and SORT2 options are present to support the
query optimizer in performing joins.
<productname>Postgres</productname> can always
evaluate a join (i.e., processing a clause with two tuple
@ -294,9 +328,8 @@ MYBOXES.description !== "0,0,1,1"::box
be worth the complexity involved.
</para>
<para>
The last two pieces of the specification are present so
the query optimizer can estimate result sizes. If a
clause of the form:
The RESTRICT and JOIN options assist the query optimizer in estimating
result sizes. If a clause of the form:
<programlisting>
MYBOXES.description &lt;&lt;&lt; "0,0,1,1"::box
</programlisting>
@ -310,7 +343,7 @@ MYBOXES.description &lt;&lt;&lt; "0,0,1,1"::box
data types and returns a floating point number. The
query optimizer simply calls this function, passing the
parameter "0,0,1,1" and multiplies the result by the relation
size to get the desired expected number of instances.
size to get the expected number of instances.
</para>
<para>
Similarly, when the operands of the operator both contain
@ -318,7 +351,7 @@ MYBOXES.description &lt;&lt;&lt; "0,0,1,1"::box
size of the resulting join. The function join_proc will
return another floating point number which will be multiplied
by the cardinalities of the two classes involved to
compute the desired expected result size.
compute the expected result size.
</para>
<para>
The difference between the function

25
doc/src/sgml/syntax.sgml
View File

@ -315,12 +315,11 @@ UNCOMMITTED UNNAMED
<para>
A <firstterm>comment</firstterm>
is an arbitrary sequence of characters following double dashes up to the end
of the line. We also support double-slashes as comments, e.g.:
is an arbitrary sequence of characters beginning with double dashes
and extending to the end of the line, e.g.:
<programlisting>
-- This is a standard SQL comment
// And this is another supported comment style, like C++
</programlisting>
We also support C-style block comments, e.g.:
@ -331,6 +330,9 @@ We also support C-style block comments, e.g.:
comment
*/
</programlisting>
A comment beginning with "/*" extends to the first occurrence of "*/".
</para>
</sect1>
@ -340,17 +342,22 @@ We also support C-style block comments, e.g.:
<para>
Names in SQL are sequences of less than NAMEDATALEN alphanumeric characters,
starting with an alphabetic character. By default, NAMEDATALEN is set
to 32, but at the time the system is built, NAMEDATALEN can be changed
to 32 (but at the time the system is built, NAMEDATALEN can be changed
by changing the <literal>#define</literal> in
src/backend/include/postgres.h.
src/backend/include/postgres.h).
Underscore ("_") is considered an alphabetic character.
</para>
<para>
In some contexts, names may contain other characters if surrounded
by double quotes. For example, table or column names may contain otherwise
disallowed characters such as spaces, ampersands, etc. using this
technique.
Names containing other characters may be formed by surrounding them
with double quotes. For example, table or column names may contain
otherwise disallowed characters such as spaces, ampersands, etc. if
quoted. Quoting a name also makes it case-sensitive,
whereas unquoted names are always folded to lower case. For example,
the names <literal>FOO</literal>, <literal>foo</literal>
and <literal>"foo"</literal> are
considered the same by <productname>Postgres</productname>, but
<literal>"Foo"</literal> is a different name.
</para>
</sect1>