database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-12-19 17:02:53 +03:00
Code Activity

Allow AS to be omitted when specifying an output column name in SELECT

Browse Source 
(or RETURNING), but only when the output name is not any SQL keyword.
This seems as close as we can get to the standard's syntax without a
great deal of thrashing.  Original patch by Hiroshi Saito, amended by me.
This commit is contained in:
Tom Lane
2008-02-15 22:17:06 +00:00
parent cc80f0a340
commit e67867b26c
10 changed files with 119 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
doc/src/sgml/ref/delete.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/delete.sgml,v 1.32 2007/11/28 15:42:31 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/delete.sgml,v 1.33 2008/02/15 22:17:06 tgl Exp $
PostgreSQL documentation
-->
@@ -23,7 +23,7 @@ PostgreSQL documentation
DELETE FROM [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
[ USING <replaceable class="PARAMETER">usinglist</replaceable> ]
[ WHERE <replaceable class="PARAMETER">condition</replaceable> | WHERE CURRENT OF <replaceable class="PARAMETER">cursor_name</replaceable> ]
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ AS <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
</synopsis>
</refsynopsisdiv>

4
doc/src/sgml/ref/insert.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/insert.sgml,v 1.35 2007/01/31 23:26:04 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/insert.sgml,v 1.36 2008/02/15 22:17:06 tgl Exp $
PostgreSQL documentation
-->
@@ -22,7 +22,7 @@ PostgreSQL documentation
<synopsis>
INSERT INTO <replaceable class="PARAMETER">table</replaceable> [ ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) ]
{ DEFAULT VALUES | VALUES ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) [, ...] | <replaceable class="PARAMETER">query</replaceable> }
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ AS <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
</synopsis>
</refsynopsisdiv>

87
doc/src/sgml/ref/select.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.102 2007/11/28 15:42:31 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.103 2008/02/15 22:17:06 tgl Exp $
PostgreSQL documentation
-->
@@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replaceable> [, ...] ) ] ]
* | <replaceable class="parameter">expression</replaceable> [ AS <replaceable class="parameter">output_name</replaceable> ] [, ...]
* | <replaceable class="parameter">expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...]
[ FROM <replaceable class="parameter">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="parameter">condition</replaceable> ]
[ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...] ]
@@ -477,23 +477,45 @@ HAVING <replaceable class="parameter">condition</replaceable>
<literal>SELECT</> and <literal>FROM</>) specifies expressions
that form the output rows of the <command>SELECT</command>
statement. The expressions can (and usually do) refer to columns
computed in the <literal>FROM</> clause. Using the clause
<literal>AS <replaceable
class="parameter">output_name</replaceable></literal>, another
name can be specified for an output column. This name is
primarily used to label the column for display. It can also be
used to refer to the column's value in <literal>ORDER BY</> and
<literal>GROUP BY</> clauses, but not in the <literal>WHERE</> or
<literal>HAVING</> clauses; there you must write out the
expression instead.
computed in the <literal>FROM</> clause.
</para>
<para>
Just as in a table, every output column of a <command>SELECT</command>
has a name. In a simple <command>SELECT</command> this name is just
used to label the column for display, but when the <command>SELECT</>
is a sub-query of a larger query, the name is seen by the larger query
as the column name of the virtual table produced by the sub-query.
To specify the name to use for an output column, write
<literal>AS</> <replaceable class="parameter">output_name</replaceable>
after the column's expression. (You can omit <literal>AS</literal>,
but only if the desired output name does not match any
<productname>PostgreSQL</productname> keyword (see <xref
linkend="sql-keywords-appendix">). For protection against possible
future keyword additions, it is recommended that you always either
write <literal>AS</literal> or double-quote the output name.)
If you do not specify a column name, a name is chosen automatically
by <productname>PostgreSQL</productname>. If the column's expression
is a simple column reference then the chosen name is the same as that
column's name; in more complex cases a generated name looking like
<literal>?column<replaceable>N</>?</literal> is usually chosen.
</para>
<para>
An output column's name can be used to refer to the column's value in
<literal>ORDER BY</> and <literal>GROUP BY</> clauses, but not in the
<literal>WHERE</> or <literal>HAVING</> clauses; there you must write
out the expression instead.
</para>
<para>
Instead of an expression, <literal>*</literal> can be written in
the output list as a shorthand for all the columns of the selected
rows. Also, one can write <literal><replaceable
rows. Also, you can write <literal><replaceable
class="parameter">table_name</replaceable>.*</literal> as a
shorthand for the columns coming from just that table.
shorthand for the columns coming from just that table. In these
cases it is not possible to specify new names with <literal>AS</>;
the output column names will be the same as the table columns' names.
</para>
</refsect2>
@@ -661,17 +683,17 @@ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC |
<para>
The ordinal number refers to the ordinal (left-to-right) position
of the result column. This feature makes it possible to define an
of the output column. This feature makes it possible to define an
ordering on the basis of a column that does not have a unique
name. This is never absolutely necessary because it is always
possible to assign a name to a result column using the
possible to assign a name to an output column using the
<literal>AS</> clause.
</para>
<para>
It is also possible to use arbitrary expressions in the
<literal>ORDER BY</literal> clause, including columns that do not
appear in the <command>SELECT</command> result list. Thus the
appear in the <command>SELECT</command> output list. Thus the
following statement is valid:
<programlisting>
SELECT name FROM distributors ORDER BY code;
@@ -684,8 +706,8 @@ SELECT name FROM distributors ORDER BY code;
<para>
If an <literal>ORDER BY</> expression is a simple name that
matches both a result column name and an input column name,
<literal>ORDER BY</> will interpret it as the result column name.
matches both an output column name and an input column name,
<literal>ORDER BY</> will interpret it as the output column name.
This is the opposite of the choice that <literal>GROUP BY</> will
make in the same situation. This inconsistency is made to be
compatible with the SQL standard.
@@ -1135,16 +1157,25 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
</refsect2>
<refsect2>
<title>The <literal>AS</literal> Key Word</title>
<title>Omitting the <literal>AS</literal> Key Word</title>
<para>
In the SQL standard, the optional key word <literal>AS</> is just
noise and can be omitted without affecting the meaning. The
<productname>PostgreSQL</productname> parser requires this key
word when renaming output columns because the type extensibility
features lead to parsing ambiguities without it.
<literal>AS</literal> is optional in <literal>FROM</literal>
items, however.
In the SQL standard, the optional key word <literal>AS</> can be
omitted before an output column name whenever the new column name
is a valid column name (that is, not the same as any reserved
keyword). <productname>PostgreSQL</productname> is slightly more
restrictive: <literal>AS</> is required if the new column name
matches any keyword at all, reserved or not. Recommended practice is
to use <literal>AS</> or double-quote output column names, to prevent
any possible conflict against future keyword additions.
</para>
<para>
In <literal>FROM</literal> items, both the standard and
<productname>PostgreSQL</productname> allow <literal>AS</> to
be omitted before an alias that is an unreserved keyword. But
this is impractical for output column names, because of syntactic
ambiguities.
</para>
</refsect2>
@@ -1153,7 +1184,7 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
<para>
In the SQL-92 standard, an <literal>ORDER BY</literal> clause can
only use result column names or numbers, while a <literal>GROUP
only use output column names or numbers, while a <literal>GROUP
BY</literal> clause can only use expressions based on input column
names. <productname>PostgreSQL</productname> extends each of
these clauses to allow the other choice as well (but it uses the
@@ -1161,7 +1192,7 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
<productname>PostgreSQL</productname> also allows both clauses to
specify arbitrary expressions. Note that names appearing in an
expression will always be taken as input-column names, not as
result-column names.
output-column names.
</para>
<para>

4
doc/src/sgml/ref/select_into.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.39 2007/01/09 02:14:10 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select_into.sgml,v 1.40 2008/02/15 22:17:06 tgl Exp $
PostgreSQL documentation
-->
@@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
SELECT [ ALL | DISTINCT [ ON ( <replaceable class="PARAMETER">expression</replaceable> [, ...] ) ] ]
* | <replaceable class="PARAMETER">expression</replaceable> [ AS <replaceable class="PARAMETER">output_name</replaceable> ] [, ...]
* | <replaceable class="PARAMETER">expression</replaceable> [ [ AS ] <replaceable class="PARAMETER">output_name</replaceable> ] [, ...]
INTO [ TEMPORARY | TEMP ] [ TABLE ] <replaceable class="PARAMETER">new_table</replaceable>
[ FROM <replaceable class="PARAMETER">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="PARAMETER">condition</replaceable> ]

4
doc/src/sgml/ref/update.sgml
View File

@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.45 2007/11/28 15:42:31 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.46 2008/02/15 22:17:06 tgl Exp $
PostgreSQL documentation
-->
@@ -25,7 +25,7 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <rep
( <replaceable class="PARAMETER">column</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) } [, ...]
[ FROM <replaceable class="PARAMETER">fromlist</replaceable> ]
[ WHERE <replaceable class="PARAMETER">condition</replaceable> | WHERE CURRENT OF <replaceable class="PARAMETER">cursor_name</replaceable> ]
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ AS <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
[ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
</synopsis>
</refsynopsisdiv>