Oracle 18c

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CREATE TABLE t(id INT PRIMARY KEY, col INT  DEFAULT 10)
INSERT INTO t(id, col) VALUES(1, NULL)
1 rows affected

SELECT * FROM t;

ID
COL

1
null

CREATE TABLE t2(id INT PRIMARY KEY, col INT  DEFAULT ON NULL 10);
INSERT INTO t2(id, col) VALUES(1, NULL)
1 rows affected

SELECT * FROM t2;

ID
COL

1
10