Introduction to Oracle TRUNCATE

What is Oracle TRUNCATE?

Oracle TRUNCATE is a SQL command used to quickly and efficiently remove all rows from a table or a cluster. It is an alternative to the DELETE command, but it performs the operation more swiftly by bypassing the transaction log. TRUNCATE is a DDL (Data Definition Language) operation and cannot be rolled back.

The syntax for TRUNCATE is as follows:

TRUNCATE TABLE table_name;

Key Points about Oracle TRUNCATE:

• TRUNCATE is designed to remove all the rows from a table or cluster, leaving its structure intact.
• Unlike the DELETE command, TRUNCATE does not generate any undo logs, making it faster and more resource-efficient.
• TRUNCATE releases the storage space associated with the table, improving performance by reducing storage fragmentation.
• TRUNCATE resets any sequence numbers associated with the table.
• TRUNCATE cannot be rolled back, so it is essential to use it with caution.
• TRUNCATE is typically used when you want to remove all the data from a table and do not require the option to undo the operation.

Examples illustrating the usage of Oracle TRUNCATE:

Example 1: Basic usage of TRUNCATE

TRUNCATE TABLE employees;

This statement will remove all the rows from the "employees" table, but the table structure and other associated objects will remain unaffected.

Example 2: Truncating a table with foreign key constraints

TRUNCATE TABLE orders CASCADE;

In this example, the TRUNCATE command will remove all rows from the "orders" table, and because we specified the CASCADE clause, it will also remove the dependent rows from any child tables that have foreign key constraints pointing to the "orders" table.

Example 3: Truncating multiple tables simultaneously

TRUNCATE TABLE table1, table2, table3;

The above statement will truncate multiple tables, i.e., "table1", "table2", and "table3" in a single command.

Conclusion

Oracle TRUNCATE is a powerful SQL command that efficiently removes all rows from a table or cluster. It offers performance benefits over the DELETE command and releases storage space as well. Care must be taken while using TRUNCATE as it cannot be rolled back.