SQL (Structured Query Language) comes with a variety of features that make it a powerful and versatile language for interacting with relational databases. Here are some key features of SQL:
- Data Query Language (DQL):
- SQL provides a comprehensive set of commands for querying data from databases. The SELECT statement is the primary DQL command used to retrieve specific information from one or more tables.
- Data Definition Language (DDL):
- SQL includes commands for defining and managing the structure of a database. Key DDL commands include:
- CREATE: Used to create database objects such as tables, indexes, and views.
- ALTER: Used to modify the structure of existing database objects.
- DROP: Used to delete database objects.
- Data Manipulation Language (DML):
- SQL supports commands for manipulating data stored in the database. Key DML commands include:
- INSERT: Adds new records to a table.
- UPDATE: Modifies existing records in a table.
- DELETE: Removes records from a table.
- Data Control Language (DCL):
- DCL commands are used to manage access to data within the database. Key DCL commands include:
- GRANT: Provides specific privileges to users or roles.
- REVOKE: Removes specific privileges from users or roles.
- Transaction Control:
- SQL supports transactions, which are sequences of one or more SQL statements that are executed as a single unit. Transactions ensure data consistency and integrity. Key transaction control commands include COMMIT, ROLLBACK, and SAVEPOINT.
- Constraints:
- SQL allows the definition of constraints on tables to ensure data integrity. Common constraints include PRIMARY KEY, FOREIGN KEY, CHECK, and UNIQUE.
- Joins:
- SQL provides the ability to combine rows from different tables using joins. Common types of joins include INNER JOIN, LEFT JOIN, and RIGHT JOIN.
- Indexes:
- Indexes are used to improve the performance of database queries by providing a faster way to look up data based on certain columns.
- Views:
- Views allow users to create a virtual table based on the result of a SELECT query. They provide a way to simplify complex queries and encapsulate data access logic.
- Stored Procedures and Functions:
- SQL supports the creation of stored procedures and functions, which are precompiled and stored in the database for efficient execution. They help modularize and reuse code.
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