--
-- UPDATE ... SET <col> = DEFAULT;
--
CREATE TABLE update_test (
    a   INT DEFAULT 10,
    b   INT
);
INSERT INTO update_test VALUES (5, 10);
INSERT INTO update_test VALUES (10, 15);
SELECT * FROM update_test;
 a  | b  
----+----
  5 | 10
 10 | 15
(2 rows)

UPDATE update_test SET a = DEFAULT, b = DEFAULT;
SELECT * FROM update_test;
 a  | b 
----+---
 10 |  
 10 |  
(2 rows)

-- aliases for the UPDATE target table
UPDATE update_test AS t SET b = 10 WHERE t.a = 10;
SELECT * FROM update_test;
 a  | b  
----+----
 10 | 10
 10 | 10
(2 rows)

UPDATE update_test t SET b = t.b + 10 WHERE t.a = 10;
SELECT * FROM update_test;
 a  | b  
----+----
 10 | 20
 10 | 20
(2 rows)

-- if an alias for the target table is specified, don't allow references
-- to the original table name
BEGIN;
SET LOCAL add_missing_from = false;
UPDATE update_test AS t SET b = update_test.b + 10 WHERE t.a = 10;
ERROR:  invalid reference to FROM-clause entry for table "update_test"
LINE 1: UPDATE update_test AS t SET b = update_test.b + 10 WHERE t.a...
                                        ^
HINT:  Perhaps you meant to reference the table alias "t".
ROLLBACK;
DROP TABLE update_test;