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Support all SQL:2011 options for window frame clauses.

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This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions.  We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion.  That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value.  Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that.  (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)

The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types.  Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.

In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011.  As far as I can see, we are now fully
up to spec on window framing options.

Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.

Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.

Oliver Ford, reviewed and whacked around some by me

Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
This commit is contained in:
Tom Lane
2018-02-07 00:06:50 -05:00
parent 2320945731
commit 0a459cec96
38 changed files with 4297 additions and 392 deletions
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181
doc/src/sgml/btree.sgml
View File

@ -207,7 +207,7 @@
<para>
As shown in <xref linkend="xindex-btree-support-table"/>, btree defines
one required and one optional support function.
one required and two optional support functions.
</para>
<para>
@ -252,6 +252,185 @@
<filename>src/include/utils/sortsupport.h</filename>.
</para>
<indexterm>
<primary>in_range support functions</primary>
</indexterm>
<indexterm>
<primary>support functions</primary>
<secondary>in_range</secondary>
</indexterm>
<para>
Optionally, a btree operator family may
provide <firstterm>in_range</firstterm> support function(s), registered
under support function number 3. These are not used during btree index
operations; rather, they extend the semantics of the operator family so
that it can support window clauses containing
the <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>PRECEDING</literal>
and <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>FOLLOWING</literal> frame bound types (see
<xref linkend="syntax-window-functions"/>). Fundamentally, the extra
information provided is how to add or subtract
an <replaceable>offset</replaceable> value in a way that is compatible
with the family's data ordering.
</para>
<para>
An <function>in_range</function> function must have the signature
<synopsis>
in_range(<replaceable>val</replaceable> type1, <replaceable>base</replaceable> type1, <replaceable>offset</replaceable> type2, <replaceable>sub</replaceable> bool, <replaceable>less</replaceable> bool)
returns bool
</synopsis>
<replaceable>val</replaceable> and <replaceable>base</replaceable> must be
of the same type, which is one of the types supported by the operator
family (i.e., a type for which it provides an ordering).
However, <replaceable>offset</replaceable> could be of a different type,
which might be one otherwise unsupported by the family. An example is
that the built-in <literal>time_ops</literal> family provides
an <function>in_range</function> function that
has <replaceable>offset</replaceable> of type <type>interval</type>.
A family can provide <function>in_range</function> functions for any of
its supported types and one or more <replaceable>offset</replaceable>
types. Each <function>in_range</function> function should be entered
in <structname>pg_amproc</structname>
with <structfield>amproclefttype</structfield> equal to <type>type1</type>
and <structfield>amprocrighttype</structfield> equal to <type>type2</type>.
</para>
<para>
The essential semantics of an <function>in_range</function> function
depend on the two boolean flag parameters. It should add or
subtract <replaceable>base</replaceable>
and <replaceable>offset</replaceable>, then
compare <replaceable>val</replaceable> to the result, as follows:
<itemizedlist>
<listitem>
<para>
if <literal>!</literal><replaceable>sub</replaceable> and
<literal>!</literal><replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&gt;=</literal>
(<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <literal>!</literal><replaceable>sub</replaceable>
and <replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable>
and <literal>!</literal><replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&gt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable> and <replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
</itemizedlist>
Before doing so, the function should check the sign
of <replaceable>offset</replaceable>: if it is less than zero, raise
error <literal>ERRCODE_INVALID_PRECEDING_FOLLOWING_SIZE</literal> (22013)
with error text like <quote>invalid preceding or following size in window
function</quote>. (This is required by the SQL standard, although
nonstandard operator families might perhaps choose to ignore this
restriction, since there seems to be little semantic necessity for it.)
This requirement is delegated to the <function>in_range</function>
function so that the core code needn't understand what <quote>less than
zero</quote> means for a particular data type.
</para>
<para>
An additional expectation is that <function>in_range</function> functions
should, if practical, avoid throwing an error
if <replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>
or <replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable> would overflow.
The correct comparison result can be determined even if that value would
be out of the data type's range. Note that if the data type includes
concepts such as <quote>infinity</quote> or <quote>NaN</quote>, extra care
may be needed to ensure that <function>in_range</function>'s results agree
with the normal sort order of the operator family.
</para>
<para>
The results of the <function>in_range</function> function must be
consistent with the sort ordering imposed by the operator family.
To be precise, given any fixed values of <replaceable>offset</replaceable>
and <replaceable>sub</replaceable>, then:
<itemizedlist>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is true for some <replaceable>val1</replaceable>
and <replaceable>base</replaceable>, it must be true for
every <replaceable>val2</replaceable> <literal>&lt;=</literal>
<replaceable>val1</replaceable> with the
same <replaceable>base</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is false for some <replaceable>val1</replaceable>
and <replaceable>base</replaceable>, it must be false for
every <replaceable>val2</replaceable> <literal>&gt;=</literal>
<replaceable>val1</replaceable> with the
same <replaceable>base</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is true for some <replaceable>val</replaceable>
and <replaceable>base1</replaceable>, it must be true for
every <replaceable>base2</replaceable> <literal>&gt;=</literal>
<replaceable>base1</replaceable> with the
same <replaceable>val</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is false for some <replaceable>val</replaceable>
and <replaceable>base1</replaceable>, it must be false for
every <replaceable>base2</replaceable> <literal>&lt;=</literal>
<replaceable>base1</replaceable> with the
same <replaceable>val</replaceable>.
</para>
</listitem>
</itemizedlist>
Analogous statements with inverted conditions hold
when <replaceable>less</replaceable> = false.
</para>
<para>
If the type being ordered (<type>type1</type>) is collatable,
the appropriate collation OID will be passed to
the <function>in_range</function> function, using the standard
PG_GET_COLLATION() mechanism.
</para>
<para>
<function>in_range</function> functions need not handle NULL inputs, and
typically will be marked strict.
</para>
</sect1>
<sect1 id="btree-implementation">

5
doc/src/sgml/func.sgml
View File

@ -14729,8 +14729,9 @@ SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
partition through the last peer of the current row. This is
likely to give unhelpful results for <function>last_value</function> and
sometimes also <function>nth_value</function>. You can redefine the frame by
adding a suitable frame specification (<literal>RANGE</literal> or
<literal>ROWS</literal>) to the <literal>OVER</literal> clause.
adding a suitable frame specification (<literal>RANGE</literal>,
<literal>ROWS</literal> or <literal>GROUPS</literal>) to
the <literal>OVER</literal> clause.
See <xref linkend="syntax-window-functions"/> for more information
about frame specifications.
</para>

117
doc/src/sgml/ref/select.sgml
View File

@ -859,19 +859,28 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
The <replaceable class="parameter">frame_clause</replaceable> can be one of
<synopsis>
{ RANGE | ROWS } <replaceable>frame_start</replaceable>
{ RANGE | ROWS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable>
{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
</synopsis>
where <replaceable>frame_start</replaceable> and <replaceable>frame_end</replaceable> can be
one of
where <replaceable>frame_start</replaceable>
and <replaceable>frame_end</replaceable> can be one of
<synopsis>
UNBOUNDED PRECEDING
<replaceable>value</replaceable> PRECEDING
<replaceable>offset</replaceable> PRECEDING
CURRENT ROW
<replaceable>value</replaceable> FOLLOWING
<replaceable>offset</replaceable> FOLLOWING
UNBOUNDED FOLLOWING
</synopsis>
and <replaceable>frame_exclusion</replaceable> can be one of
<synopsis>
EXCLUDE CURRENT ROW
EXCLUDE GROUP
EXCLUDE TIES
EXCLUDE NO OTHERS
</synopsis>
If <replaceable>frame_end</replaceable> is omitted it defaults to <literal>CURRENT
@ -879,8 +888,10 @@ UNBOUNDED FOLLOWING
<replaceable>frame_start</replaceable> cannot be <literal>UNBOUNDED FOLLOWING</literal>,
<replaceable>frame_end</replaceable> cannot be <literal>UNBOUNDED PRECEDING</literal>,
and the <replaceable>frame_end</replaceable> choice cannot appear earlier in the
above list than the <replaceable>frame_start</replaceable> choice &mdash; for example
<literal>RANGE BETWEEN CURRENT ROW AND <replaceable>value</replaceable>
above list of <replaceable>frame_start</replaceable>
and <replaceable>frame_end</replaceable> options than
the <replaceable>frame_start</replaceable> choice does &mdash; for example
<literal>RANGE BETWEEN CURRENT ROW AND <replaceable>offset</replaceable>
PRECEDING</literal> is not allowed.
</para>
@ -888,33 +899,72 @@ UNBOUNDED FOLLOWING
The default framing option is <literal>RANGE UNBOUNDED PRECEDING</literal>,
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
CURRENT ROW</literal>; it sets the frame to be all rows from the partition start
up through the current row's last peer (a row that <literal>ORDER
BY</literal> considers equivalent to the current row, or all rows if there
is no <literal>ORDER BY</literal>).
up through the current row's last <firstterm>peer</firstterm> (a row
that the window's <literal>ORDER BY</literal> clause considers
equivalent to the current row), or all rows if there
is no <literal>ORDER BY</literal>.
In general, <literal>UNBOUNDED PRECEDING</literal> means that the frame
starts with the first row of the partition, and similarly
<literal>UNBOUNDED FOLLOWING</literal> means that the frame ends with the last
row of the partition (regardless of <literal>RANGE</literal> or <literal>ROWS</literal>
mode). In <literal>ROWS</literal> mode, <literal>CURRENT ROW</literal>
means that the frame starts or ends with the current row; but in
<literal>RANGE</literal> mode it means that the frame starts or ends with
the current row's first or last peer in the <literal>ORDER BY</literal> ordering.
The <replaceable>value</replaceable> <literal>PRECEDING</literal> and
<replaceable>value</replaceable> <literal>FOLLOWING</literal> cases are currently only
allowed in <literal>ROWS</literal> mode. They indicate that the frame starts
or ends with the row that many rows before or after the current row.
<replaceable>value</replaceable> must be an integer expression not
containing any variables, aggregate functions, or window functions.
The value must not be null or negative; but it can be zero, which
selects the current row itself.
row of the partition, regardless
of <literal>RANGE</literal>, <literal>ROWS</literal>
or <literal>GROUPS</literal> mode.
In <literal>ROWS</literal> mode, <literal>CURRENT ROW</literal> means
that the frame starts or ends with the current row; but
in <literal>RANGE</literal> or <literal>GROUPS</literal> mode it means
that the frame starts or ends with the current row's first or last peer
in the <literal>ORDER BY</literal> ordering.
The <replaceable>offset</replaceable> <literal>PRECEDING</literal> and
<replaceable>offset</replaceable> <literal>FOLLOWING</literal> options
vary in meaning depending on the frame mode.
In <literal>ROWS</literal> mode, the <replaceable>offset</replaceable>
is an integer indicating that the frame starts or ends that many rows
before or after the current row.
In <literal>GROUPS</literal> mode, the <replaceable>offset</replaceable>
is an integer indicating that the frame starts or ends that many peer
groups before or after the current row's peer group, where
a <firstterm>peer group</firstterm> is a group of rows that are
equivalent according to <literal>ORDER BY</literal>.
In <literal>RANGE</literal> mode, use of
an <replaceable>offset</replaceable> option requires that there be
exactly one <literal>ORDER BY</literal> column in the window definition.
Then the frame contains those rows whose ordering column value is no
more than <replaceable>offset</replaceable> less than
(for <literal>PRECEDING</literal>) or more than
(for <literal>FOLLOWING</literal>) the current row's ordering column
value. In these cases the data type of
the <replaceable>offset</replaceable> expression depends on the data
type of the ordering column. For numeric ordering columns it is
typically of the same type as the ordering column, but for datetime
ordering columns it is an <type>interval</type>.
In all these cases, the value of the <replaceable>offset</replaceable>
must be non-null and non-negative. Also, while
the <replaceable>offset</replaceable> does not have to be a simple
constant, it cannot contain variables, aggregate functions, or window
functions.
</para>
<para>
Beware that the <literal>ROWS</literal> options can produce unpredictable
The <replaceable>frame_exclusion</replaceable> option allows rows around
the current row to be excluded from the frame, even if they would be
included according to the frame start and frame end options.
<literal>EXCLUDE CURRENT ROW</literal> excludes the current row from the
frame.
<literal>EXCLUDE GROUP</literal> excludes the current row and its
ordering peers from the frame.
<literal>EXCLUDE TIES</literal> excludes any peers of the current
row from the frame, but not the current row itself.
<literal>EXCLUDE NO OTHERS</literal> simply specifies explicitly the
default behavior of not excluding the current row or its peers.
</para>
<para>
Beware that the <literal>ROWS</literal> mode can produce unpredictable
results if the <literal>ORDER BY</literal> ordering does not order the rows
uniquely. The <literal>RANGE</literal> options are designed to ensure that
rows that are peers in the <literal>ORDER BY</literal> ordering are treated
alike; all peer rows will be in the same frame.
uniquely. The <literal>RANGE</literal> and <literal>GROUPS</literal>
modes are designed to ensure that rows that are peers in
the <literal>ORDER BY</literal> ordering are treated alike: all rows of
a given peer group will be in the frame or excluded from it.
</para>
<para>
@ -1981,17 +2031,6 @@ SELECT distributors.* WHERE distributors.name = 'Westward';
</para>
</refsect2>
<refsect2>
<title><literal>WINDOW</literal> Clause Restrictions</title>
<para>
The SQL standard provides additional options for the window
<replaceable class="parameter">frame_clause</replaceable>.
<productname>PostgreSQL</productname> currently supports only the
options listed above.
</para>
</refsect2>
<refsect2>
<title><literal>LIMIT</literal> and <literal>OFFSET</literal></title>

144
doc/src/sgml/syntax.sgml
View File

@ -1802,20 +1802,27 @@ FROM generate_series(1,10) AS s(i);
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
[ <replaceable class="parameter">frame_clause</replaceable> ]
</synopsis>
and the optional <replaceable class="parameter">frame_clause</replaceable>
The optional <replaceable class="parameter">frame_clause</replaceable>
can be one of
<synopsis>
{ RANGE | ROWS } <replaceable>frame_start</replaceable>
{ RANGE | ROWS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable>
{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
</synopsis>
where <replaceable>frame_start</replaceable> and <replaceable>frame_end</replaceable> can be
one of
where <replaceable>frame_start</replaceable>
and <replaceable>frame_end</replaceable> can be one of
<synopsis>
UNBOUNDED PRECEDING
<replaceable>value</replaceable> PRECEDING
<replaceable>offset</replaceable> PRECEDING
CURRENT ROW
<replaceable>value</replaceable> FOLLOWING
<replaceable>offset</replaceable> FOLLOWING
UNBOUNDED FOLLOWING
</synopsis>
and <replaceable>frame_exclusion</replaceable> can be one of
<synopsis>
EXCLUDE CURRENT ROW
EXCLUDE GROUP
EXCLUDE TIES
EXCLUDE NO OTHERS
</synopsis>
</para>
@ -1856,11 +1863,14 @@ UNBOUNDED FOLLOWING
The <replaceable class="parameter">frame_clause</replaceable> specifies
the set of rows constituting the <firstterm>window frame</firstterm>, which is a
subset of the current partition, for those window functions that act on
the frame instead of the whole partition. The frame can be specified in
either <literal>RANGE</literal> or <literal>ROWS</literal> mode; in either case, it
runs from the <replaceable>frame_start</replaceable> to the
<replaceable>frame_end</replaceable>. If <replaceable>frame_end</replaceable> is omitted,
it defaults to <literal>CURRENT ROW</literal>.
the frame instead of the whole partition. The set of rows in the frame
can vary depending on which row is the current row. The frame can be
specified in <literal>RANGE</literal>, <literal>ROWS</literal>
or <literal>GROUPS</literal> mode; in each case, it runs from
the <replaceable>frame_start</replaceable> to
the <replaceable>frame_end</replaceable>.
If <replaceable>frame_end</replaceable> is omitted, the end defaults
to <literal>CURRENT ROW</literal>.
</para>
<para>
@ -1871,24 +1881,91 @@ UNBOUNDED FOLLOWING
</para>
<para>
In <literal>RANGE</literal> mode, a <replaceable>frame_start</replaceable> of
<literal>CURRENT ROW</literal> means the frame starts with the current row's
first <firstterm>peer</firstterm> row (a row that <literal>ORDER BY</literal> considers
equivalent to the current row), while a <replaceable>frame_end</replaceable> of
<literal>CURRENT ROW</literal> means the frame ends with the last equivalent
<literal>ORDER BY</literal> peer. In <literal>ROWS</literal> mode, <literal>CURRENT ROW</literal> simply means
the current row.
In <literal>RANGE</literal> or <literal>GROUPS</literal> mode,
a <replaceable>frame_start</replaceable> of
<literal>CURRENT ROW</literal> means the frame starts with the current
row's first <firstterm>peer</firstterm> row (a row that the
window's <literal>ORDER BY</literal> clause sorts as equivalent to the
current row), while a <replaceable>frame_end</replaceable> of
<literal>CURRENT ROW</literal> means the frame ends with the current
row's last peer row.
In <literal>ROWS</literal> mode, <literal>CURRENT ROW</literal> simply
means the current row.
</para>
<para>
The <replaceable>value</replaceable> <literal>PRECEDING</literal> and
<replaceable>value</replaceable> <literal>FOLLOWING</literal> cases are currently only
allowed in <literal>ROWS</literal> mode. They indicate that the frame starts
or ends the specified number of rows before or after the current row.
<replaceable>value</replaceable> must be an integer expression not
In the <replaceable>offset</replaceable> <literal>PRECEDING</literal>
and <replaceable>offset</replaceable> <literal>FOLLOWING</literal> frame
options, the <replaceable>offset</replaceable> must be an expression not
containing any variables, aggregate functions, or window functions.
The value must not be null or negative; but it can be zero, which
just selects the current row.
The meaning of the <replaceable>offset</replaceable> depends on the
frame mode:
<itemizedlist>
<listitem>
<para>
In <literal>ROWS</literal> mode,
the <replaceable>offset</replaceable> must yield a non-null,
non-negative integer, and the option means that the frame starts or
ends the specified number of rows before or after the current row.
</para>
</listitem>
<listitem>
<para>
In <literal>GROUPS</literal> mode,
the <replaceable>offset</replaceable> again must yield a non-null,
non-negative integer, and the option means that the frame starts or
ends the specified number of <firstterm>peer groups</firstterm>
before or after the current row's peer group, where a peer group is a
set of rows that are equivalent in the <literal>ORDER BY</literal>
ordering. (If there is no <literal>ORDER BY</literal>, the whole
partition is one peer group.)
</para>
</listitem>
<listitem>
<para>
In <literal>RANGE</literal> mode, these options require that
the <literal>ORDER BY</literal> clause specify exactly one column.
The <replaceable>offset</replaceable> specifies the maximum
difference between the value of that column in the current row and
its value in preceding or following rows of the frame. The data type
of the <replaceable>offset</replaceable> expression varies depending
on the data type of the ordering column. For numeric ordering
columns it is typically of the same type as the ordering column,
but for datetime ordering columns it is an <type>interval</type>.
For example, if the ordering column is of type <type>date</type>
or <type>timestamp</type>, one could write <literal>RANGE BETWEEN
'1 day' PRECEDING AND '10 days' FOLLOWING</literal>.
The <replaceable>offset</replaceable> is still required to be
non-null and non-negative, though the meaning
of <quote>non-negative</quote> depends on its data type.
</para>
</listitem>
</itemizedlist>
In any case, the distance to the end of the frame is limited by the
distance to the end of the partition, so that for rows near the partition
ends the frame might contain fewer rows than elsewhere.
</para>
<para>
Notice that in both <literal>ROWS</literal> and <literal>GROUPS</literal>
mode, <literal>0 PRECEDING</literal> and <literal>0 FOLLOWING</literal>
are equivalent to <literal>CURRENT ROW</literal>. This normally holds
in <literal>RANGE</literal> mode as well, for an appropriate
data-type-specific meaning of <quote>zero</quote>.
</para>
<para>
The <replaceable>frame_exclusion</replaceable> option allows rows around
the current row to be excluded from the frame, even if they would be
included according to the frame start and frame end options.
<literal>EXCLUDE CURRENT ROW</literal> excludes the current row from the
frame.
<literal>EXCLUDE GROUP</literal> excludes the current row and its
ordering peers from the frame.
<literal>EXCLUDE TIES</literal> excludes any peers of the current
row from the frame, but not the current row itself.
<literal>EXCLUDE NO OTHERS</literal> simply specifies explicitly the
default behavior of not excluding the current row or its peers.
</para>
<para>
@ -1896,9 +1973,9 @@ UNBOUNDED FOLLOWING
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
CURRENT ROW</literal>. With <literal>ORDER BY</literal>, this sets the frame to be
all rows from the partition start up through the current row's last
<literal>ORDER BY</literal> peer. Without <literal>ORDER BY</literal>, all rows of the partition are
included in the window frame, since all rows become peers of the current
row.
<literal>ORDER BY</literal> peer. Without <literal>ORDER BY</literal>,
this means all rows of the partition are included in the window frame,
since all rows become peers of the current row.
</para>
<para>
@ -1906,9 +1983,14 @@ UNBOUNDED FOLLOWING
<replaceable>frame_start</replaceable> cannot be <literal>UNBOUNDED FOLLOWING</literal>,
<replaceable>frame_end</replaceable> cannot be <literal>UNBOUNDED PRECEDING</literal>,
and the <replaceable>frame_end</replaceable> choice cannot appear earlier in the
above list than the <replaceable>frame_start</replaceable> choice &mdash; for example
<literal>RANGE BETWEEN CURRENT ROW AND <replaceable>value</replaceable>
above list of <replaceable>frame_start</replaceable>
and <replaceable>frame_end</replaceable> options than
the <replaceable>frame_start</replaceable> choice does &mdash; for example
<literal>RANGE BETWEEN CURRENT ROW AND <replaceable>offset</replaceable>
PRECEDING</literal> is not allowed.
But, for example, <literal>ROWS BETWEEN 7 PRECEDING AND 8
PRECEDING</literal> is allowed, even though it would never select any
rows.
</para>
<para>

60
doc/src/sgml/xindex.sgml
View File

@ -401,7 +401,8 @@
</para>
<para>
B-trees require a single support function, and allow a second one to be
B-trees require a comparison support function,
and allow two additional support functions to be
supplied at the operator class author's option, as shown in <xref
linkend="xindex-btree-support-table"/>.
The requirements for these support functions are explained further in
@ -433,6 +434,13 @@
</entry>
<entry>2</entry>
</row>
<row>
<entry>
Compare a test value to a base value plus/minus an offset, and return
true or false according to the comparison result (optional)
</entry>
<entry>3</entry>
</row>
</tbody>
</tgroup>
</table>
@ -971,7 +979,8 @@ DEFAULT FOR TYPE int8 USING btree FAMILY integer_ops AS
OPERATOR 4 >= ,
OPERATOR 5 > ,
FUNCTION 1 btint8cmp(int8, int8) ,
FUNCTION 2 btint8sortsupport(internal) ;
FUNCTION 2 btint8sortsupport(internal) ,
FUNCTION 3 in_range(int8, int8, int8, boolean, boolean) ;
CREATE OPERATOR CLASS int4_ops
DEFAULT FOR TYPE int4 USING btree FAMILY integer_ops AS
@ -982,7 +991,8 @@ DEFAULT FOR TYPE int4 USING btree FAMILY integer_ops AS
OPERATOR 4 >= ,
OPERATOR 5 > ,
FUNCTION 1 btint4cmp(int4, int4) ,
FUNCTION 2 btint4sortsupport(internal) ;
FUNCTION 2 btint4sortsupport(internal) ,
FUNCTION 3 in_range(int4, int4, int4, boolean, boolean) ;
CREATE OPERATOR CLASS int2_ops
DEFAULT FOR TYPE int2 USING btree FAMILY integer_ops AS
@ -993,7 +1003,8 @@ DEFAULT FOR TYPE int2 USING btree FAMILY integer_ops AS
OPERATOR 4 >= ,
OPERATOR 5 > ,
FUNCTION 1 btint2cmp(int2, int2) ,
FUNCTION 2 btint2sortsupport(internal) ;
FUNCTION 2 btint2sortsupport(internal) ,
FUNCTION 3 in_range(int2, int2, int2, boolean, boolean) ;
ALTER OPERATOR FAMILY integer_ops USING btree ADD
-- cross-type comparisons int8 vs int2
@ -1042,7 +1053,13 @@ ALTER OPERATOR FAMILY integer_ops USING btree ADD
OPERATOR 3 = (int2, int4) ,
OPERATOR 4 >= (int2, int4) ,
OPERATOR 5 > (int2, int4) ,
FUNCTION 1 btint24cmp(int2, int4) ;
FUNCTION 1 btint24cmp(int2, int4) ,
-- cross-type in_range functions
FUNCTION 3 in_range(int4, int4, int8, boolean, boolean) ,
FUNCTION 3 in_range(int4, int4, int2, boolean, boolean) ,
FUNCTION 3 in_range(int2, int2, int8, boolean, boolean) ,
FUNCTION 3 in_range(int2, int2, int4, boolean, boolean) ;
]]>
</programlisting>
@ -1180,6 +1197,39 @@ SELECT * FROM mytable ORDER BY somecol USING ~&lt;~;
then array equality is supported, but not ordering comparisons.
</para>
<para>
Another SQL feature that requires even more data-type-specific knowledge
is the <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>PRECEDING</literal>/<literal>FOLLOWING</literal> framing option
for window functions (see <xref linkend="syntax-window-functions"/>).
For a query such as
<programlisting>
SELECT sum(x) OVER (ORDER BY x RANGE BETWEEN 5 PRECEDING AND 10 FOLLOWING)
FROM mytable;
</programlisting>
it is not sufficient to know how to order by <literal>x</literal>;
the database must also understand how to <quote>subtract 5</quote> or
<quote>add 10</quote> to the current row's value of <literal>x</literal>
to identify the bounds of the current window frame. Comparing the
resulting bounds to other rows' values of <literal>x</literal> is
possible using the comparison operators provided by the B-tree operator
class that defines the <literal>ORDER BY</literal> ordering &mdash; but
addition and subtraction operators are not part of the operator class, so
which ones should be used? Hard-wiring that choice would be undesirable,
because different sort orders (different B-tree operator classes) might
need different behavior. Therefore, a B-tree operator class can specify
an <firstterm>in_range</firstterm> support function that encapsulates the
addition and subtraction behaviors that make sense for its sort order.
It can even provide more than one in_range support function, in case
there is more than one data type that makes sense to use as the offset
in <literal>RANGE</literal> clauses.
If the B-tree operator class associated with the window's <literal>ORDER
BY</literal> clause does not have a matching in_range support function,
the <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>PRECEDING</literal>/<literal>FOLLOWING</literal>
option is not supported.
</para>
<para>
Another important point is that an equality operator that
appears in a hash operator family is a candidate for hash joins,