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From: Thom Brown <[email protected]>
To: pgsql-docs <[email protected]>
Subject: Aggregate expression syntax
Date: Tue, 20 Jan 2015 13:50:22 +0000
Message-ID: <CAA-aLv7A9uqH=U=Czp5UBbukJW6_ip7NDZsAMf6-F72s6Ls+LA@mail.gmail.com> (raw)
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Hi all,

Looking at the syntax for aggregate expressions in the docs, it seems the
first three forms could perhaps be merged since the ALL and DISTINCT
keywords are effectively optional.

Currently:

aggregate_name (expression [ , ... ] [ order_by_clause ] ) [ FILTER ( WHERE
filter_clause ) ]
aggregate_name (ALL expression [ , ... ] [ order_by_clause ] ) [ FILTER (
WHERE filter_clause ) ]
aggregate_name (DISTINCT expression [ , ... ] [ order_by_clause ] ) [
FILTER ( WHERE filter_clause ) ]

Proposed:

aggregate_name ( [ ALL | DISTINCT ] expression [ , ... ] [ order_by_clause
] ) [ FILTER ( WHERE filter_clause ) ]

I've also found a precedent for this on the SELECT statement page:

[ { UNION | INTERSECT | EXCEPT } [ ALL | DISTINCT ] select ]

Patch attached with the proposed change.

Opinions?

Thom


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Attachments:

  [text/x-patch] agg_exp_docs.patch (2.5K, 3-agg_exp_docs.patch)
  download | inline diff:
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 4b81b08..4f8a43b 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1574,9 +1574,7 @@ sqrt(2)
     syntax of an aggregate expression is one of the following:
 
 <synopsis>
-<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
-<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
-<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
+<replaceable>aggregate_name</replaceable> ( [ ALL | DISTINCT ] <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
 <replaceable>aggregate_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
 <replaceable>aggregate_name</replaceable> ( [ <replaceable>expression</replaceable> [ , ... ] ] ) WITHIN GROUP ( <replaceable>order_by_clause</replaceable> ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
 </synopsis>
@@ -1591,14 +1589,12 @@ sqrt(2)
    </para>
 
    <para>
-    The first form of aggregate expression invokes the aggregate
-    once for each input row.
-    The second form is the same as the first, since
-    <literal>ALL</literal> is the default.
-    The third form invokes the aggregate once for each distinct value
-    of the expression (or distinct set of values, for multiple expressions)
-    found in the input rows.
-    The fourth form invokes the aggregate once for each input row; since no
+    The first form of aggregate expression with the <literal>ALL</literal>
+    keyword (the default) invokes the aggregate once for each input row.
+    Specifying <literal>DISTINCT</literal> invokes the aggregate once for
+    each distinct value of the expression (or distinct set of values, for
+    multiple expressions) found in the input rows.
+    The second form invokes the aggregate once for each input row; since no
     particular input value is specified, it is generally only useful
     for the <function>count(*)</function> aggregate function.
     The last form is used with <firstterm>ordered-set</> aggregate

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