On 2026-06-12 Fr 6:50 PM, Baji Shaik wrote:
Hi,
While testing the new COPY JSON format, I noticed the column list
ordering is ignored when the list mentions every column of the
relation. CSV and TEXT formats respect the order; JSON does not.
CREATE TABLE t (a int, b int);
INSERT INTO t VALUES (1, 2);
COPY t (b, a) TO STDOUT WITH (FORMAT csv); -- "2,1"
COPY t (b, a) TO STDOUT WITH (FORMAT json); -- {"a":1,"b":2}
-- expected: {"b":2,"a":1}
In BeginCopyTo() (commit 7dadd38cda9), the JSON path builds a custom
TupleDesc only when the column list is shorter than the relation:
if (rel && list_length(cstate->attnumlist) < tupDesc->natts)
When the user provides a full column list reordered, list_length
equals natts, so the natural TupleDesc is reused.
Fix is to extend the condition to also fire when an explicit column list
was supplied (attnamelist != NIL).
All 245 regression tests pass.
This seems to be a harmless enough change, and if we're going to do it
we should do it now.
OTOH, any application that relies on a particular field ordering in JSON
data is broken by design, IMNSHO.
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com
