ROLLBACK; BEGIN;

CREATE TABLE example_table (
	test_column TEXT unique
)
;

INSERT INTO example_table VALUES ('abc')
ON CONFLICT (test_column) DO NOTHING
;

CREATE PROCEDURE example_works (
	test_column_in TEXT
) AS
$$
#variable_conflict use_variable
BEGIN

INSERT INTO example_table (test_column) VALUES (test_column_in)
ON CONFLICT (test_column) DO NOTHING
;

END
$$
LANGUAGE plpgsql
;

CALL example_works('xyz');

SELECT * FROM example_table
;

CREATE PROCEDURE example_breaks (
	test_column TEXT
-- ^ note: the new declaration name is the same as the column name
) AS
$$
#variable_conflict use_variable
BEGIN
-- ^ normally, name conflicts would be resolved successully this way...

INSERT INTO example_table (test_column) --  `variable_conflict` is working here √
VALUES (test_column) --  `variable_conflict` is working here √
ON CONFLICT (test_column) DO NOTHING --  `variable_conflict` is NOT working here X @ `(test_column)`
;

END
$$
LANGUAGE plpgsql
;

CALL example_breaks('qwe');


/*
[42P10] ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification
PL/pgSQL function example_breaks(text) line 6 at SQL statement
*/

ROLLBACK;