What is SQL?
SQL is a non-procedural language, which means users specify what data they want, not how to retrieve it. The database engine decides the best way to execute the query.
SQL is supported by most database systems such as MySQL, Oracle, SQL Server, and PostgreSQL.
Uses of SQL
SQL is used to:
- Create and modify database structures
- Insert, update, and delete data
- Retrieve data from one or more tables
- Control access to data
- Manage transactions
Categories of SQL Commands
SQL commands are divided into the following categories:
1. Data Definition Language (DDL)
DDL commands define the structure of the database.
Common DDL commands:
- CREATE
- ALTER
- DROP
- TRUNCATE
- RENAME
2. Data Manipulation Language (DML)
DML commands are used to manage data stored in tables.
Common DML commands:
- INSERT
- UPDATE
- DELETE
- SELECT
3. Data Control Language (DCL)
DCL commands control access permissions.
Common DCL commands:
- GRANT
- REVOKE
4. Transaction Control Language (TCL)
TCL commands manage transactions.
Common TCL commands:
- COMMIT
- ROLLBACK
- SAVEPOINT
Basic SQL Queries
- Retrieving data using SELECT
- Filtering records using WHERE
- Sorting results using ORDER BY
- Grouping data using GROUP BY
- Applying conditions using HAVING
SQL Constraints
Constraints enforce rules on data.
Common constraints:
- PRIMARY KEY
- FOREIGN KEY
- UNIQUE
- NOT NULL
- CHECK
- DEFAULT
Advantages of SQL
- Easy to learn and use
- Platform-independent
- Supports large databases
- Secure data handling
- Standardized language
Limitations of SQL
- Complex queries can be difficult to write
- Limited procedural capabilities
- Performance issues with huge datasets
Conclusion
Structured Query Language is the backbone of relational databases. It provides a powerful and standardized way to manage data efficiently. Mastering SQL is essential for B.Sc. IT students and anyone pursuing a career in database management or software development.