How to add default value in Oracle?

Adding a default value in Oracle can be a useful feature when it comes to providing a predetermined value for a column in a table if no explicit value is specified during an insert operation. In this article, we will explore how to add a default value in Oracle and answer some common questions related to this topic.

How to add a default value in Oracle?

To add a default value in Oracle, you can use the DEFAULT clause while defining the column during table creation or by altering an existing table using the ALTER TABLE statement.

Here’s an example of adding a default value during table creation:

“`
CREATE TABLE employees (
id NUMBER PRIMARY KEY,
name VARCHAR2(50),
department VARCHAR2(50) DEFAULT ‘IT’
);
“`

In the above example, the column ‘department’ is defined with a default value of ‘IT’. If no department value is specified during an insert operation, Oracle will automatically assign ‘IT’ to it.

To add a default value to an existing table, you can use the ALTER TABLE statement with the MODIFY clause:

“`
ALTER TABLE employees MODIFY department DEFAULT ‘IT’;
“`

This statement will set the default value of the ‘department’ column to ‘IT’.

Frequently Asked Questions:

1. Can I add a default value to a column that already contains data?

No, you cannot add a default value to a column that already contains data. The default value only applies to new rows that are inserted into the table.

2. Can I override the default value when inserting data into a column?

Yes, you can explicitly specify a value during an insert operation, which will override the default value for that particular row.

3. Can I remove a default value from a column?

Yes, you can remove a default value from a column by using the ALTER TABLE statement with the MODIFY clause and omitting the DEFAULT keyword.

4. Can I add a default value to an existing column with NULL values?

Yes, you can add a default value to an existing column that contains NULL values. The default value will be applied to new rows inserted into the table without explicitly specifying a value for that column.

5. Can I use a function or expression as a default value?

Yes, you can use a function or expression as a default value in Oracle. For example, you can set the default value of a column to the current date using the SYSDATE function.

6. Can I add a default value to a column with an existing constraint?

No, you cannot add a default value to a column that has an existing constraint. You will need to drop the constraint, add the default value, and then recreate the constraint.

7. Can I have different default values for different rows in the same column?

No, the default value applies to all new rows inserted into the table. If you need different default values, you may consider using triggers or application-level logic.

8. Can I modify the default value of a column?

Yes, you can modify the default value of a column by using the ALTER TABLE statement with the MODIFY clause and specifying the new default value.

9. Can I have a default value for a primary key column?

No, primary key columns cannot have default values since they must be unique and not null.

10. Can I add a default value to a column in a specific tablespace?

No, default values are not defined at the tablespace level but at the column level. The default value will apply to all rows in the table, regardless of the tablespace.

11. Can I add a default value to a column in a specific schema?

Yes, you can add a default value to a column in a specific schema. The schema-specific default value will apply to all tables within that schema.

12. Can I add a default value to a column that is part of a composite primary key?

Yes, you can add a default value to a column that is part of a composite primary key. However, when inserting data into the table, you will need to explicitly specify values for all columns in the primary key. The default value will only be used if the primary key column is not explicitly specified.

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