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Don Burleson Blog 







NOT NULL Constraint Tips

Oracle Database Tips by Donald BurlesonDecember 16, 2015

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
   (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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