SQL
2 mins read
What is Database?
A database is an organized collection of data that is stored and accessed electronically. Databases are designed to manage and manipulate large amounts of structured information efficiently. They support operations such as querying, updating, and managing data.
What is SQL?
SQL stands for Structured Query Language. It is a standard language for database management systems. SQL can perform various tasks like creating/dropping a table, manipulating data, and setting permissions for users.
What is DBMS and how it is different from RDBMS?
| DBMS | RDBMS |
|---|---|
| A DBMS is software that provides an interface to create, read, update, and delete data in a database. | An RDBMS is a type of DBMS that stores data in a structured format using rows and columns (tables). |
| Manages data efficiently and allows users to perform multiple tasks with ease. | Focuses on relational data, supporting SQL for database access and manipulation. |
| Can handle different types of databases like hierarchical, network, or object-oriented databases. | Ensures ACID (Atomicity, Consistency, Isolation, Durability) properties and supports relationships between tables. |
| Examples: Oracle, MongoDB, and Microsoft Access. | Examples: MySQL, PostgreSQL, Microsoft SQL Server, and Oracle Database. |
What are SQL Commands? Explain types of SQL Commands.
SQL commands are the instructions used to communicate with a database to perform tasks, functions, and queries with data. SQL commands can be used to search the database and to do other functions like creating tables, adding data to tables, modifying data, and dropping tables.
They can be categorized into several types based on their functionality:
1. DDL (Data Definition Language)
CREATE: Creates new database objects like tables, indexes, or views.
ALTER: Modifies existing database objects.
DROP: Deletes database objects.
TRUNCATE: Removes all records from a table but not the table itself.
2. DML (Data Manipulation Language)
SELECT: Retrieves data from the database.
INSERT: Adds new rows to a table.
UPDATE: Modifies existing data in a table.
DELETE: Removes rows from a table.
3. DCL (Data Control Language)
GRANT: Gives user permissions to perform tasks.
REVOKE: Removes user permissions.
4. TCL (Transaction Control Language)
COMMIT: Saves all transactions to the database.
ROLLBACK: Undoes transactions that have not been committed.
5. DQL (Data Query Language)
SELECT: Retrieves data from the database (often considered part of DML)