Difference Between DML and TCL

Data Manipulation Language (DML) and Transaction Control Language (TCL) are critical subsets of SQL (Structured Query Language). Both play essential roles in managing and controlling data in a database, but they serve different purposes. In this article, we will explore about the Difference between DML and TCL in detail.

Prerequisite:

DDL, DML, TCL and DCL 

What is Data Manipulation Language (DML) ?

DML is used to manipulate data in the database. For example, insert, update and delete instructions in SQL. 

Key DML Commands:

• SELECT – Retrieves data from the database.
• INSERT – Adds new data into the database.
• UPDATE – Modifies existing data.
• DELETE – Removes data from the database.

Advantages of DML:

• Easy Data Modification: DML commands allow users to easily modify and retrieve data as needed.
• Flexible Queries: You can use the SELECT statement with various conditions to retrieve specific records.
• Data Interaction: Allows for interaction with the database without directly altering the database schema.

Disadvantages of DML:

• No Transaction Control: While DML handles data manipulation, it does not provide control over transactions like commit or rollback.
• Potential Data Loss: Incorrect use of DELETE or UPDATE can lead to unintentional loss of data if not used cautiously.

What is Transaction Control Language (TCL) ?

TCL deals with the transactions within the database. 

Key TCL Commands

• COMMIT – Saves the changes made during a transaction.
• ROLLBACK – Reverts the database to its previous state if an error occurs.
• SAVEPOINT – Creates points within transactions to which you can rollback.
• SET TRANSACTION – Defines properties for a new transaction.

Advantages of TCL

• Transaction Safety: Ensures that database transactions are executed correctly and consistently.
• Error Handling: In case of any failure, ROLLBACK helps prevent partial or incorrect data being saved in the database.
• Data Consistency: Maintains the integrity of data across multiple operations.

Disadvantages of TCL

• Complexity: Managing multiple transactions and ensuring proper usage of commit and rollback can become complex in large systems.
• No Data Interaction: TCL doesn't handle direct data manipulation, so it relies on DML or other SQL commands for modifying data.

Difference between DML and TCL

What is the main difference between DML and TCL?

The main difference is that DML deals with data manipulation (inserting, updating, deleting data), while TCL controls the transactions (commit, rollback) that affect the state of the database.

Can we use DML commands without TCL?

Yes, DML commands can be used without TCL, but using TCL commands such as COMMIT or ROLLBACK ensures that changes made by DML commands are either saved or reverted consistently.

What happens if we don’t use TCL commands after a DML operation?

If you don't use TCL commands, the changes made by DML might not be saved permanently or could lead to inconsistent database states in the event of a failure.

Which is more important, DML or TCL?

Both are equally important. DML allows you to interact with and manipulate data, while TCL ensures those interactions happen within a controlled and safe transaction.