Structured Query Language (SQL)

Introduction to SQL

Structured Query Language (SQL) is a standardized programming language specifically designed for managing and manipulating relational databases. It provides a systematic and efficient way to communicate with database management systems (DBMS) to perform various operations such as creating, retrieving, updating, and deleting data. SQL enables users to interact with the data stored in tables, which are organized in rows and columns, following the relational model. The language is declarative, meaning users specify what data they want without detailing how to retrieve it. SQL is widely used in various applications ranging from small-scale personal databases to large enterprise systems. The language is divided into several sublanguages, each serving a distinct purpose: Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), and Transaction Control Language (TCL). This chapter introduces these components and explains how SQL commands are structured and executed to manage database objects and data effectively.

• SQL is a standard language for managing and manipulating relational databases.
• It is declarative, focusing on what data to retrieve rather than how to retrieve it.
• SQL operates on tables organized in rows and columns.
• The language is divided into DDL, DML, DCL, and TCL sublanguages.
• SQL commands enable creation, retrieval, modification, and control of data and database structures.
• It is widely used across various domains for database management.
• 📌 SQL: Structured Query Language, a language for managing relational databases.
• 📌 Relational Database: A database structured to recognize relations among stored items of information.
• 📌 Declarative Language: A programming language that expresses the logic of computation without describing its control flow.

Data Definition Language (DDL)

Data Definition Language (DDL) is a subset of SQL commands that define and modify the structure of database objects such as tables, indexes, and schemas. These commands are essential for creating the database schema and organizing data storage. The primary DDL commands include CREATE, ALTER, and DROP. The CREATE command is used to create new tables or other database objects, specifying the columns, data types, and constraints. ALTER modifies the structure of existing tables, such as adding or deleting columns or changing data types. DROP deletes tables or other objects permanently from the database. DDL commands affect the metadata of the database and are auto-committed, meaning changes are immediately saved. Understanding DDL is crucial for designing the database layout before manipulating the data within it.

• DDL commands define and modify database structures.
• CREATE command is used to create new tables and database objects.
• ALTER command modifies existing table structures.
• DROP command deletes tables or database objects permanently.
• DDL commands affect the schema and metadata of the database.
• Changes made by DDL commands are auto-committed.
• 📌 CREATE: SQL command to create database objects.
• 📌 ALTER: SQL command to modify existing database objects.
• 📌 DROP: SQL command to delete database objects.