Oddity in COPY FROM handling of check constraints on partition tables

Hi,

While updating the tuple-routing-for-foreign-partitions patch, I noticed
oddity in the COPY FROM handling of check constraints on partition
tables.  Here is an example:

postgres=# create table pt (a int, b int) partition by list (a);
CREATE TABLE
postgres=# create table p1 partition of pt for values in (1);
CREATE TABLE
postgres=# alter table p1 add check (b > 0);
ALTER TABLE
postgres=# copy pt from '/home/pgsql/copy_data.csv' (format csv,
delimiter ',');
COPY 1
postgres=# select tableoid::regclass, * from pt;
 tableoid | a | b
----------+---+----
 p1       | 1 | -1
(1 row)

where the file '/home/pgsql/copy_data.csv' has a single row data

$ cat /home/pgsql/copy_data.csv
1,-1

which violates the constraint on the column b (ie, b > 0), so this
should abort.  The reason for that is because CopyFrom looks at the
parent relation's constraints, not the partition's constraints, when
checking the constraint against the input row.

Attached is a patch for fixing this issue.

Best regards,
Etsuro Fujita