DATABASE LANGUAGE

 

 

 

1. Data Definition Language

 

DDL stands for Data Definition Language. It is used to define database structure or pattern. It is used to create schema, tables, indexes, constraints, etc. in the database. Using the DDL statements, you can create the skeleton of the database. Data definition language is used to store the information of metadata like the number of tables and schemas, their names, indexes, columns in each table, constraints, etc.
Here are some commands that come under DDL:

• Create: It is used to create objects in the database.

• Alter: It is used to alter the structure of the database.

• Drop: It is used to delete objects from the database.

• Truncate: It is used to remove all records from a table.

2. Data Manipulation Language

 
DML stands for Data Manipulation Language. It is used for accessing and manipulating data in a database. It handles user request Here are some commands that come under DML:

• Insert: It is used to insert data into a table.

• Update: It is used to update existing data within a table.

• Delete: It is used to delete all records from a table.

3. Data Control Language

 

DCL stands for Data Control Language. It is used to retrieve the stored or saved data. The DCL execution is transactional. It also has rollback parameters. Here are some tasks that come under DCL:

• Grant: It is used to give user access privileges to a database.
• Revoke: It is used to take back permissions from the user.

4. Transaction Control Language

 
TCL is used to run the changes made by the DML statement. TCL can be grouped into a logical transaction. Here are some tasks that come under TCL:

• Commit: It is used to save the transaction on the database.
• Rollback: It is used to restore the database to original since the last Commit. 

Data Independence

 

Data independence can be explained using the three-schema architecture. Data independence refers characteristic of being able to modify the schema at one level of the database system without altering the schema at the next higher level.

There are two types of data independence

1. Logical Data Independence
• Logical data independence refers characteristic of being able to change the conceptual schema without having to change the external schema.
• Logical data independence is used to separate the external level from the conceptual view.
• If we do any changes in the conceptual view of the data, then the user view of the data would not be affected.
• Logical data independence occurs at the user interface level.

2. Physical Data Independence
• Physical data independence can be defined as the capacity to change the internal schema without  having to change the conceptual schema.
• If we do any changes in the storage size of the database system server, then the Conceptual structure of the database will not be affected.
• Physical data independence is used to separate conceptual levels from the internal levels.
• Physical data independence occurs at the logical interface level.