From: Bruce Momjian <bruce@momjian.us>
Date: Thu, 1 Sep 2022 02:19:06 +0000 (-0400)
Subject: doc:  use FILTER in aggregate example
X-Git-Tag: REL_13_9~66
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d55fdfb554348ffd8e3afc61d62523a8f7d4a78e;p=thirdparty%2Fpostgresql.git

doc:  use FILTER in aggregate example

Reported-by: michal.palenik@freemap.sk

Discussion: https://postgr.es/m/163499710897.684.7420075366995883688@wrigleys.postgresql.org

Backpatch-through: 10
---

diff --git a/doc/src/sgml/query.sgml b/doc/src/sgml/query.sgml
index d58be9c969d..1606396c000 100644
--- a/doc/src/sgml/query.sgml
+++ b/doc/src/sgml/query.sgml
@@ -728,19 +728,20 @@ SELECT city, max(temp_lo)
     which gives us one output row per city.  Each aggregate result is
     computed over the table rows matching that city.
     We can filter these grouped
-    rows using <literal>HAVING</literal>:
+    rows using <literal>HAVING</literal> and the output count using
+    <literal>FILTER</literal>:
 
 <programlisting>
-SELECT city, max(temp_lo)
+SELECT city, max(temp_lo), count(*) FILTER (WHERE temp_lo &lt; 30)
     FROM weather
     GROUP BY city
     HAVING max(temp_lo) &lt; 40;
 </programlisting>
 
 <screen>
-  city   | max
----------+-----
- Hayward |  37
+  city   | max | count
+---------+-----+-------
+ Hayward |  37 |     5
 (1 row)
 </screen>
 
@@ -750,7 +751,7 @@ SELECT city, max(temp_lo)
     names begin with <quote><literal>S</literal></quote>, we might do:
 
 <programlisting>
-SELECT city, max(temp_lo)
+SELECT city, max(temp_lo), count(*) FILTER (WHERE temp_lo &lt; 30)
     FROM weather
     WHERE city LIKE 'S%'            -- <co id="co.tutorial-agg-like"/>
     GROUP BY city