database/postgres
database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-05-01 01:04:50 +03:00
Code

Document strange jsonb sort order for empty top level arrays

Browse Source 
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
This commit is contained in:
Andrew Dunstan 2025-01-03 09:23:46 -05:00
parent e28033fe1a
commit 30f0176263
2 changed files with 9 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
doc/src/sgml/json.sgml
View File

@ -584,12 +584,13 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @@ '$.tags[*] == "qui"';
The <literal>btree</literal> ordering for <type>jsonb</type> datums is seldom
of great interest, but for completeness it is:
<synopsis>
<replaceable>Object</replaceable> > <replaceable>Array</replaceable> > <replaceable>Boolean</replaceable> > <replaceable>Number</replaceable> > <replaceable>String</replaceable> > <replaceable>Null</replaceable>
<replaceable>Object</replaceable> > <replaceable>Array</replaceable> > <replaceable>Boolean</replaceable> > <replaceable>Number</replaceable> > <replaceable>String</replaceable> > <replaceable>null</replaceable>
<replaceable>Object with n pairs</replaceable> > <replaceable>object with n - 1 pairs</replaceable>
<replaceable>Array with n elements</replaceable> > <replaceable>array with n - 1 elements</replaceable>
</synopsis>
with the exception that (for historical reasons) an empty top level array sorts less than <replaceable>null</replaceable>.
Objects with equal numbers of pairs are compared in the order:
<synopsis>
<replaceable>key-1</replaceable>, <replaceable>value-1</replaceable>, <replaceable>key-2</replaceable> ...

7
src/backend/utils/adt/jsonb_util.c
View File

@ -246,6 +246,13 @@ compareJsonbContainers(JsonbContainer *a, JsonbContainer *b)
*/
if (va.val.array.rawScalar != vb.val.array.rawScalar)
res = (va.val.array.rawScalar) ? -1 : 1;
/*
* There should be an "else" here, to prevent us from
* overriding the above, but we can't change the sort
* order now, so there is a mild anomaly that an empty
* top level array sorts less than null.
*/
if (va.val.array.nElems != vb.val.array.nElems)
res = (va.val.array.nElems > vb.val.array.nElems) ? 1 : -1;
break;