Can We Change Data Type in Oracle?


Angela Bailey

Can We Change Data Type in Oracle?

When working with databases, it’s common to come across situations where the data type of a column needs to be changed. In Oracle, changing the data type of a column is possible, but it requires careful consideration and planning.

Why Change Data Type?

There are various reasons why you might need to change the data type of a column in an Oracle database. Some common scenarios include:

  • When the existing data type is no longer appropriate for the data being stored.
  • When the column needs to accommodate a wider range of values.
  • When you want to optimize storage or performance by using a more suitable data type.

The ALTER TABLE Statement

In Oracle, the ALTER TABLE statement is used to modify existing tables. To change the data type of a column, you can use the MODIFY clause along with the ALTER TABLE statement.


ALTER TABLE table_name MODIFY (column_name new_data_type);

Note: It’s important to ensure that any existing data in the column can be successfully converted to the new data type. Otherwise, it may result in data loss or errors during conversion.

Data Type Conversion

Oracle provides built-in functions that allow you to convert data from one type to another during an ALTER TABLE operation. These functions help ensure that the conversion is performed safely and accurately.

The TO_CHAR Function:

The TO_CHAR function converts a value of any datatype into a text string representation.

Syntax: TO_CHAR(value, format)

The TO_NUMBER Function:

The TO_NUMBER function converts a text string representation of a number into an actual numeric value.

Syntax: TO_NUMBER(value, format)

The TO_DATE Function:

The TO_DATE function converts a text string representation of a date into an actual date value.

Syntax: TO_DATE(value, format)

Considerations and Limitations

  • Changing the data type of a column may require appropriate permissions or privileges.
  • Certain data type conversions may result in loss of precision or truncation of data.
  • If the column is part of an index or a constraint, it may need to be dropped and recreated after the data type change.
  • Changing the data type can be time-consuming for large tables with lots of data. It’s recommended to perform such changes during off-peak hours.


In Oracle, changing the data type of a column is possible using the ALTER TABLE statement. However, it’s crucial to carefully plan and consider the implications before making any changes.

Remember to take into account factors such as existing data, conversions, permissions, and potential limitations. By following best practices and using appropriate conversion functions, you can successfully change the data type while ensuring minimal disruption to your database operations.

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