diff options
| author | Andrew Dunstan | 2025-01-03 14:23:46 +0000 |
|---|---|---|
| committer | Andrew Dunstan | 2025-01-03 15:36:30 +0000 |
| commit | 30f017626308a06cf0c0c82a706a1ba1b07df34a (patch) | |
| tree | bab5af8cca336d73ead7f8490fb6f58205646273 | |
| parent | e28033fe1af8037e0fec8bb3a32fabbe18ac06b1 (diff) | |
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
| -rw-r--r-- | doc/src/sgml/json.sgml | 3 | ||||
| -rw-r--r-- | src/backend/utils/adt/jsonb_util.c | 7 |
2 files changed, 9 insertions, 1 deletions
diff --git a/doc/src/sgml/json.sgml b/doc/src/sgml/json.sgml index 54648c459c1..206eadb8f7b 100644 --- a/doc/src/sgml/json.sgml +++ b/doc/src/sgml/json.sgml @@ -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> ... diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c index 806d1aa3a98..773f3690c7b 100644 --- a/src/backend/utils/adt/jsonb_util.c +++ b/src/backend/utils/adt/jsonb_util.c @@ -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; |