DDL vs DML
When it comes to working with databases, understanding the
different types of SQL commands is crucial. Two fundamental types of SQL
commands are Data Definition Language (DDL) and Data Manipulation Language
(DML). In this article, we will delve into the differences between DDL and DML,
their functions, and when to use them.
Table of Contents
1. What is DDL?
DDL, or Data Definition Language, is a subset of SQL
commands that primarily deals with the management of database structures. It is
used to define and manage the structure that holds the data in a database. DDL
commands are not concerned with data manipulation but rather focus on creating,
modifying, and deleting database objects such as tables, indexes, and views.
1.1 DDL Commands
Some common DDL commands include:
1.2 Use Cases of DDL
DDL is typically used during the initial setup of a database
or when changes to the database structure are required. For example, when
creating new tables to store specific types of data, or altering the structure
of existing tables to accommodate new requirements.
2. What is DML?
DML, or Data Manipulation Language, is another subset of SQL
commands that deals with the manipulation of data stored within the database.
Unlike DDL, DML commands are used to interact with the data itself, such as
inserting, retrieving, updating, and deleting records within the tables.
2.1 DML Commands
Common DML commands include:
2.2 Use Cases of DML
DML commands are frequently used to interact with the data
stored in the database. For example, when inserting new records into a table,
retrieving specific data based on user queries, updating existing records with
new information, or deleting unwanted data from the database.
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3. Key Differences Between DDL and DML
When working with databases, it's essential to understand
the key differences between DDL and DML.
3.1 Purpose
The primary purpose of DDL is to define and manage the
database structure, while DML is used to manipulate the data stored within the
database.
3.2 Syntax
DDL commands focus on the structure and organization of the
database and use commands like CREATE, ALTER, and DROP. DML commands, on the
other hand, deal with the data itself and use commands like INSERT, SELECT,
UPDATE, and DELETE.
3.3 Execution Time
DDL commands are typically executed less frequently than DML
commands. DDL commands are often executed during the initial setup or when
structural changes are needed. DML commands, on the other hand, are executed
more frequently as they are involved in day-to-day data manipulation.
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3.4 Transaction Control
DDL commands are auto-committed, meaning they are executed
immediately and cannot be rolled back. In contrast, DML commands can be rolled
back if they are part of a transaction, allowing for greater control and data
integrity.
4. Understanding Data Definition Language (DDL)
4.1 Creating Database Objects
One of the essential functions of DDL is to create various
database objects, such as tables, indexes, and views. Creating a table involves
specifying the column names, data types, and any constraints required for the
table.
4.2 Modifying Database Objects
DDL also allows for the modification of existing database
objects. For example, you can add or delete columns in a table or change the
data type of a column.
4.3 Deleting Database Objects
Lastly, DDL enables the deletion of unnecessary database
objects. This can involve removing entire tables or indexes that are no longer
needed.
5. Exploring Data Manipulation Language (DML)
5.1 Inserting Data
One of the fundamental DML commands is INSERT. It allows you
to add new records to a table with specific values for each column.
5.2 Retrieving Data
SELECT is another crucial DML command that allows you to
retrieve data from one or more tables based on specified criteria. This is
often done using conditions and joins.
5.3 Updating Data
The UPDATE command is used to modify existing records within
a table. It can change values in specific columns based on the conditions you
provide.
5.4 Deleting Data
DELETE is the DML command used to remove specific records
from a table based on given conditions.
6. Use Cases of DDL
6.1 Creating Tables
One of the primary use cases of DDL is creating new tables
within a database. When designing a new system or application, you need to
define the tables that will store the data.
6.2 Modifying Table Structure
Over time, business requirements may change, necessitating
modifications to the existing table structure. DDL commands enable you to add
or remove columns, change data types, and perform other alterations.
6.3 Deleting Tables
When certain data is no longer needed or if you are
decommissioning a part of your system, you can use DDL commands to delete
entire tables from the database.
7. Use Cases of DML
7.1 Inserting Records
DML is widely used when new data needs to be added to the
database. For example, when a new customer registers on an e-commerce website,
their information is inserted into the customer table.
7.2 Retrieving Specific Data
SELECT statements are frequently used to retrieve specific
data based on certain conditions or user queries. For instance, a search
feature on a website will use DML to fetch relevant data.
7.3 Updating Existing Records
When users change their profile information or update
preferences, DML commands are used to modify the corresponding records in the
database.
7.4 Deleting Unwanted Records
DML commands are also utilized when removing unwanted data,
such as canceling an order and removing the order details from the database.
8. Purpose and Applications of DDL and DML
8.1 DDL Use Cases
8.2 DML Use Cases
9. Syntax Differences Between DDL and DML
9.1 DDL Syntax
DDL commands typically involve the use of keywords like
CREATE, ALTER, and DROP, followed by the object name and its attributes.
9.2 DML Syntax
DML commands, such as INSERT, SELECT, UPDATE, and DELETE,
involve specifying the target table and the values or conditions to be applied.
10. Execution Time: DDL vs. DML
10.1 DDL Execution Time
DDL commands are executed immediately and are
auto-committed, making changes permanent without the option to roll back.
10.2 DML Execution Time
DML commands are executed at runtime, allowing for more
frequent execution. They are also part of transactions, providing the
possibility to roll back changes.
11. Transaction Control in DDL and DML
11.1 Transaction Control in DDL
DDL commands cannot be rolled back, as they are
automatically committed. If an error occurs during DDL execution, it can be
challenging to revert the changes.
11.2 Transaction Control in DML
DML commands can be part of a transaction and thus rolled
back if needed. This allows for better data integrity and error handling.
12. Pros and Cons of DDL
12.1 Advantages of DDL
12.2 Disadvantages of DDL
13. Pros and Cons of DML
13.1 Advantages of DML
13.2 Disadvantages of DML
14. Best Practices When Using DDL and DML
14.1 DDL Best Practices
14.2 DML Best Practices
15. Conclusion
In conclusion, DDL and DML are essential components of SQL
used to manage databases effectively. DDL focuses on defining and modifying the
database structure, while DML allows for data manipulation. Understanding the
differences between the two and when to use them is crucial for database
management and application development.
FAQs
Q1: Can DDL commands be rolled back? A1: No, DDL
commands are automatically committed and cannot be rolled back, so it's
essential to be cautious when using them.
Q2: How often should DML commands be executed? A2:
DML commands can be executed frequently, depending on the application's needs. However,
it's crucial to optimize queries and transactions to maintain database
performance.
Q3: Can DML commands modify the database structure? A3:
No, DML commands are focused on data manipulation, and they cannot alter the
database structure. For that purpose, DDL commands should be used.
Q4: Are there any alternatives to DML for data
manipulation? A4: While DML is the primary way to manipulate data
using SQL, some programming languages offer APIs to interact with databases and
perform data manipulation operations.
Q5: What is the best approach to handle database backups? A5:
Regularly schedule automated backups of the database to ensure data integrity
and minimize the risk of data loss in case of system failures or errors.
DDL refers to Data Definition Language, which are SQL
commands used to define the structure of a database. This includes commands
like CREATE, ALTER and DROP. DML refers to Data Manipulation Language, which
are SQL commands used to manipulate data within a database. This includes
commands like INSERT, UPDATE and DELETE.DDL (Data Definition Language) is a
standard for commands that define the structure of a database. It is used to
create, modify, and delete database objects such as tables, indexes, and users.
DML (Data Manipulation Language) is a standard for commands that manipulate
data in a database. It is used to insert, update, and delete data in a
database.
Data Definition Language (DDL) refers to the syntax used to
create and modify database objects. Data Manipulation Language (DML) refers to
the syntax used to insert, update, and delete data from a database. DDL is
typically used to create or alter the structure of a database, while DML is
used to manipulate the data within a database.Data Definition Language (DDL)
statements are used to define the structure of a database. They are used to
create and modify database objects such as tables, indexes, and users. Data
Manipulation Language (DML) statements are used to manipulate data in a
database. They are used to insert, update, delete, and select data from a
database.
DDL and DML are two different types of statements that are used to work with databases.DDL stands for Data Definition Language. DDL statements are used to create and modify database objects such as tables, indexes, and users. DML stands for Data Manipulation Language. DML statements are used to select, insert, update, and delete data from a database.DDL (Data Definition Language) is a set of SQL commands that are used to create, modify and delete database objects such as tables, views and indexes. DML (Data Manipulation Language) is a set of SQL commands that are used to insert, update and delete data from database tables.DDL (Data Definition Language) is a set of SQL commands that are used to define the structure of a database. These commands are used to create, modify, and delete database objects such as tables, indexes, and users. DML (Data Manipulation Language) is a set of SQL commands that are used to manipulate data in a database. These commands are used to insert, update, and delete data in a database.
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