Question:
I need to understand how to add a NOT NULL constraint statement to
make sure that all rows have valid values. How do you alter a
column value to make it into a not null constraint?
NOT NULL Constraints
NOT NULL constraints are in-line constraints that
indicate that a column can not contain NULL values. The previous example of the
creation of the MY_STATUS table contained two examples of NOT NULL constraints
being defined. For example, the PERSON_ID column is defined as NOT NULL in that
example.
create table
customer
(status char(3)
not null,
val number
not null);
If you need to add a NOT NULL constraint to a table
after the fact, simply use the alter table command as in this example:
ALTER TABLE my_status MODIFY ( person_id NOT NULL);
Also note:
- You can
build
an index on NULL column values in a table.
- When copying
tables with CTAS, beware
that
NULL values many not copy properly.
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