(Oracle DB) - 6.0. Constraint

/* Constraint */
	-- Constraint is an object of a database
	-- NOT NULL, UNIQUE, PRIAMARY KEY, FOREIGN KEY, etc...
	/* NOT NULL */
CREATE TABLE ex2_6(
	col_null VARCHAR2(10),
	col_not_null VARCHAR2(10) NOT NULL
);

INSERT INTO ex2_6
	VALUES
	('AA', '')	-- ''generates ERROR
;

INSERT INTO ex2_6
	VALUES
	('AA', 'BB')
;

	/* Auto-identified Constraint by Oracle */
SELECT
	constraint_name,		-- SYS_C... (auto-identified)
	constraint_type,		-- C (Constraint)
	table_name,
	search_condition
	FROM user_constraints	-- System view
WHERE table_name = 'EX2_6'
;