ROWID FAQS

 1. What is ROWID in Oracle?

• ROWID is a unique identifier for a row in an Oracle database table.
• It provides the physical address of a row within a data block, making it a fast way to access and manipulate rows directly without needing indexes.

2. Can I use ROWID as a unique identifier for a table?

• While ROWID is unique to each row in a table, it should not be used as a logical unique identifier.
• Instead, primary keys or unique constraints are the recommended way to ensure logical uniqueness, as ROWID is based on physical storage, which could change if the row is moved.

3. Is ROWID portable across different databases?

• No, ROWID is not portable. It’s tied to the physical location of the row in the current database and will change if the data is exported/imported or the database is moved to another system.

4. How can I retrieve the ROWID of a row?

• You can retrieve the ROWID of a row by including it in your SELECT query, like so:

SELECT ROWID, column1, column2 FROM table_name WHERE condition;

5. How is ROWID structured?

• ROWID is an 18-character string that is broken down into several components: datafile number, block number, row number, and object ID (representing the table or cluster).

6. Can I use ROWID for updates or deletes?

• Yes, you can use ROWID to target specific rows for updates or deletes. For example:

UPDATE table_name SET column1 = 'value' WHERE ROWID = 'AAAFx9AAEAAAAJ0AAA';

This allows you to efficiently access and modify specific rows.

7. What happens if a row is deleted or moved?

• If a row is deleted, its ROWID becomes invalid. If the row is moved (e.g., due to database reorganization), its ROWID will change because the physical location of the row will be different.

8. Can I rely on ROWID for data integrity?

• No, ROWID is based on physical storage and should not be used to ensure data integrity or as a business key.
• It does not provide a logical identifier and can change if the row's physical storage is modified.

9. How does ROWID impact performance?

• ROWID is one of the fastest ways to access rows, as it directly references the physical location of a row.
• It avoids the need for index lookup, making it more efficient for accessing data, especially in large tables.

10. Can I create an index on ROWID?

• In general, creating an index on ROWID is unnecessary because ROWID is already the most efficient way to access a row.
• However, Oracle automatically uses ROWID for internal optimizations in queries.

11. What is the difference between ROWID and UROWID?

• ROWID is the physical address of a row, while UROWID (Universal ROWID) is used for large object (LOB) data types and for handling rows in partitioned tables or with object types.
•  UROWID can be larger than the standard ROWID.

12. Can ROWID be used in joins?

• Yes, ROWID can be used in joins. For example, you can compare rows in the same table by using ROWID:

SELECT e1.first_name, e2.first_name

FROM employees e1, employees e2

WHERE e1.ROWID < e2.ROWID;

13. Can I delete duplicate rows using ROWID?

• Yes, you can use ROWID to remove duplicate rows.
• A common method is to delete all rows except the one with the minimum ROWID for each group of duplicates:

DELETE FROM employees

WHERE ROWID NOT IN (

    SELECT MIN(ROWID)

    FROM employees

    GROUP BY first_name, last_name

);

14. What happens to the ROWID if the database is reorganized?

• If the database is reorganized (e.g., a table is moved, or data is reorganized to free up space), the ROWID may change because it is tied to the physical location of the row in storage.

15. Can ROWID be used for auditing purposes?

• While ROWID can uniquely identify rows, it’s generally not recommended for auditing purposes because it is tied to the physical layout of the data and can change.
• For auditing, it's better to use timestamp-based columns or other logical identifiers.