Support all SQL:2011 options for window frame clauses.

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

1 files changed, 180 insertions, 1 deletions

diff --git a/doc/src/sgml/btree.sgml b/doc/src/sgml/btree.sgml
index 9f39edc742d..10abf90189e 100644
--- a/doc/src/sgml/btree.sgml
+++ b/doc/src/sgml/btree.sgml
@@ -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">