pgsql: Document strange jsonb sort order for empty top level arrays

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: pgsql-committers(at)lists(dot)postgresql(dot)org
Subject: pgsql: Document strange jsonb sort order for empty top level arrays
Date: 2025-01-03 15:41:30
Message-ID: E1tTjnl-002pID-Ng@gemulon.postgresql.org
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Document strange jsonb sort order for empty top level arrays

Slightly faulty logic in the original jsonb code (commit d9134d0a355)
results in an empty top level array sorting less than a json null. We
can't change the sort order now since it would affect btree indexes over
jsonb, so document the anomaly.

Backpatch to all live branches (13 .. 17)

In master, also add a code comment noting the anomaly.

Reported-by: Yan Chengpen
Reviewed-by: Jian He

Discussion: https://postgr.es/m/OSBPR01MB45199DD8DA2D1CECD50518188E272@OSBPR01MB4519.jpnprd01.prod.outlook.com

Branch
------
REL_13_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/20a344bce8949f542eb25360fe69f14aa9a05b1b

Modified Files
--------------
doc/src/sgml/json.sgml | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

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