Not null constraint

[Geek_Guest]

What would you use to place a not null constraint on a column? If the column is left blank on insertion, it should display a custom error message.

1. Rule
2. CHECK Contstraint
3. Triggers
4. Alter the table so that the column does not allow null

[debasisdas]

Alter the table so that the column does not allow null

and write a trigger to display custom eror message.

[susarlasireesha]

Alter the table so that the column does not allow null..