Q: Constraints

Hello folks!

I have a policy problem. Some of the columns in my tables are only allowed to have either the value 'Y' or the value 'N'. Null values are not allowed.

Should I have one constraint checking the value of the column and one NOT NULL constraint or should I have one and only one constraint checking both of these cases?

ALTER TABLE a ADD CONSTRAINT b CHECK (NVL (c, '-') IN ('Y', 'N'));

or

ALTER TABLE a MODIFY b NOT NULL;
ALTER TABLE a ADD CONSTRAINT b CHECK (c IN ('Y', 'N'));

???

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