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Doc: improve documentation of the JSON object aggregates.

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Say which value wins for a repeated key, and how skipped null values
interact with that and with the unique check.  Also point out that
duplicate keys behave differently for json and jsonb cases.  (I still
think that's a bug, but at least now it's documented.)

Author: shihao zhong <zhong950419@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAGRkXqTCfSu=aEUCvKDTGroEWOcyz3MCv4Xi8x1PZ1T1rEmG=Q@mail.gmail.com
Backpatch-through: 14
This commit is contained in:
Tom Lane
2026-10-14 14:00:30 -04:00
parent beff3cd009
commit 8a5f8eb456
1 changed files with 10 additions and 3 deletions
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13
doc/src/sgml/func/func-aggregate.sgml
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@@ -404,6 +404,9 @@
are coerced to text; value arguments are converted as per
<function>to_json</function> or <function>to_jsonb</function>.
Values can be null, but keys cannot.
If a key appears more than once, the <type>json</type> result keeps
every pair, while the <type>jsonb</type> result keeps only the last
value for that key.
</para></entry>
<entry>No</entry>
</row>
@@ -432,7 +435,10 @@
are coerced to text; value arguments are converted as per
<function>to_json</function> or <function>to_jsonb</function>.
The <parameter>key</parameter> cannot be null. If the
<parameter>value</parameter> is null then the entry is skipped,
<parameter>value</parameter> is null then the pair is skipped.
Duplicate keys are handled as for <function>json_object_agg</function>
and <function>jsonb_object_agg</function>, after removing any pairs
with null values.
</para></entry>
<entry>No</entry>
</row>
@@ -490,8 +496,9 @@
are coerced to text; value arguments are converted as per
<function>to_json</function> or <function>to_jsonb</function>.
The <parameter>key</parameter> cannot be null. If the
<parameter>value</parameter> is null then the entry is skipped.
If there is a duplicate key an error is thrown.
<parameter>value</parameter> is null then the pair is skipped.
If there is a duplicate key (including pairs with null values)
an error is thrown.
</para></entry>
<entry>No</entry>
</row>