by Yogi P - November 15, 2023

Difference between delete drop and truncate | Delete vs Drop vs Truncate

In the intricate world of SQL (Structured Query Language), the commands ‘DELETE,’ ‘DROP,’ and ‘TRUNCATE’ are often sources of confusion for new programmers and database administrators. While all three commands are related to the removal of data, they serve different purposes and execute distinct actions within a database.

This article seeks to provide a clear, concise explanation of each command and the differences between Delete, Drop and truncate.

DELETE Command

The DELETE command is used to remove one or more records from a table. It is a DML (Data Manipulation Language) command and can be used with a WHERE clause to specify which records should be deleted.

If no WHERE clause is provided, all records in the table will be deleted, but the table structure, as well as its columns, constraints, indexes, and so on, will remain intact.

Key Aspects of DELETE:

• Selective Removal: Can delete specific records based on a condition.
• Transaction Logs: Records the deletion of each row in transaction logs, which can slow down the operation on large datasets.
• Rollback: Allows for rollback since it logs individual row deletions.
• Triggers: Can fire triggers associated with deletion actions.

TRUNCATE Command

TRUNCATE is a DDL (Data Definition Language) command that removes all records from a table, but unlike DELETE, it does not log the removal of each record. It is faster and uses fewer system and transaction log resources.

Key Characteristics of TRUNCATE:

• Bulk Operation: Quickly removes all rows from a table, effectively “resetting” it.
• No Transaction Logs for Each Row: Does not log the deletion of each row, which is why it is faster than DELETE.
• Cannot be Rolled Back: Typically, once executed, it cannot be rolled back unless wrapped within a transaction.
• No Triggers: Does not fire any delete triggers that might be associated with the table.

DROP Command

The DROP command is also a DDL command and is used to remove an entire table or database from the system. Not only does it delete the records, but it also removes the table schema and its dependencies like constraints, indexes, triggers, and permissions.

Key Features of DROP:

• Complete Removal: Deletes the table and its structure; everything is removed from the database.
• No Transaction Logs: Does not log any details, since the entire table is de-allocated.
• Irreversible: The action is generally not reversible (unless you have a backup), and all the data and table structure are permanently deleted.
• Releases Resources: All the space allocated to the table is released back to the system.

Table Summarizing the Differences:

Understanding Through Examples

Here are some practical examples to illustrate the differences between DELETE, TRUNCATE, and DROP:

• DELETE: You have a table named ‘Orders’ and you want to delete records of orders that were canceled.

Your SQL command would be:

DELETE FROM Orders WHERE status = 'Canceled';

This command will go through the ‘Orders’ table, find all records where the status is ‘Canceled’, and delete those specific rows. All other data in the table remains unchanged.

• TRUNCATE: You want to clear all data from the ‘Orders’ table, but you intend to keep the table for future data.

You would use the TRUNCATE command:

TRUNCATE TABLE Orders;

This command removes all rows from the ‘Orders’ table quickly, but it does not log the deletion of each row, making it faster than DELETE.

• DROP: If the ‘Orders’ table is no longer needed and you want to remove it completely from the database, you would use the DROP command:

DROP TABLE Orders;

This command will remove the table structure, its data, and any associated table constraints and indexes from the database. The ‘Orders’ table will no longer exist.

Considerations in Use

• DELETE is typically used when you need to remove specific records and might need to undo this operation.
• TRUNCATE is used when you want to delete all the data from a table but keep the table structure for future use. It’s a more efficient way to delete all records from a table if you don’t need a detailed log of the deleted records.
• DROP is used when an entire table or database is to be removed. It is irreversible and should be used with caution.

Impact on Database Performance

• DELETE is the slowest operation and can significantly impact database performance if used on large tables since it logs each row deletion.
• TRUNCATE is much faster than DELETE because it does not generate individual row delete logs, making it a preferable option for large tables when you need to delete all records.
• DROP is the fastest way to remove data since it removes the entire table from the database, and no logs are generated.

Security and Permissions

Different permissions are required for each command. While DELETE only needs delete permissions on a table, TRUNCATE and DROP typically require higher-level permissions because of their more drastic impact on the database structure.

Conclusion

In summary, DELETE, TRUNCATE, and DROP are powerful SQL commands used to remove data, but they serve different purposes.

• DELETE is for selective row deletion with the option of rollback.
• TRUNCATE is a quick way to remove all records from a table without affecting the table’s structure.
• DROP completely removes a table from the database.

Understanding the implications of each command is crucial for database management and integrity, ensuring that data is manipulated appropriately and efficiently while maintaining the ability to recover from potential mistakes.