From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 11 Oct 2014 18:29:51 +0000 (-0400)
Subject: Improve documentation about JSONB array containment behavior.
X-Git-Tag: REL9_4_RC1~89
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=308ab77b89ec1662f24b5ab4013ff0d1bd4153a1;p=postgresql

Improve documentation about JSONB array containment behavior.

Per gripe from Josh Berkus.
---

diff --git a/doc/src/sgml/json.sgml b/doc/src/sgml/json.sgml
index 37dd611aeb..8feb2fbf0a 100644
--- a/doc/src/sgml/json.sgml
+++ b/doc/src/sgml/json.sgml
@@ -269,6 +269,12 @@ SELECT '"foo"'::jsonb @> '"foo"'::jsonb;
 -- The array on the right side is contained within the one on the left:
 SELECT '[1, 2, 3]'::jsonb @> '[1, 3]'::jsonb;
 
+-- Order of array elements is not significant, so this is also true:
+SELECT '[1, 2, 3]'::jsonb @> '[3, 1]'::jsonb;
+
+-- Duplicate array elements don't matter either:
+SELECT '[1, 2, 3]'::jsonb @> '[1, 2, 2]'::jsonb;
+
 -- The object with a single pair on the right side is contained
 -- within the object on the left side:
 SELECT '{"product": "PostgreSQL", "version": 9.4, "jsonb":true}'::jsonb @> '{"version":9.4}'::jsonb;
@@ -288,8 +294,10 @@ SELECT '{"foo": {"bar": "baz"}}'::jsonb @> '{"bar": "baz"}'::jsonb;  -- yields f
    The general principle is that the contained object must match the
    containing object as to structure and data contents, possibly after
    discarding some non-matching array elements or object key/value pairs
-   from the containing object.  However, the order of array elements is
-   not significant when doing a containment match.
+   from the containing object.
+   But remember that the order of array elements is not significant when
+   doing a containment match, and duplicate array elements are effectively
+   considered only once.
   </para>
 
   <para>