You can add a NOT NULL column to a table. This means that a constant expression, and not a null value, is placed in the column when the column is added. This also ensures that, for all existing rows, the new column is populated with the specified constant expression when the table is created.
Adaptive Server issues an error message if a user fails to enter a value for a NOT NULL column.
The following adds the column owner to the stores table with a default value of “unknown:”
alter table stores add owner_lname varchar(20) default "unknown" not null
The default value can be a constant expression when adding NULL columns, but it can be a constant value only when adding a NOT NULL column (as in the example above).
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