SQL 2 CREATE TABLE Command | Informatics Practices | Complete Guide скачать в хорошем качестве

SQL 2 CREATE TABLE Command | Informatics Practices | Complete Guide

Master CREATE TABLE Command in SQL | Class 11 Informatics Practices | Complete Guide Welcome to Mishant Malhotra Mathematics Classes. In this detailed lecture, we cover one of the most important topics of Class 11 Informatics Practices – the CREATE TABLE command in SQL. This video is specially designed for students who want strong conceptual clarity along with exam-oriented preparation. If you are preparing for school examinations, practical exams, viva, or simply want to understand how databases work, this complete guide will help you step by step. Structured Query Language, commonly known as SQL, is the standard language used to manage and manipulate relational databases. In Class 11 Informatics Practices, students are introduced to the basics of databases and SQL commands. Among all SQL commands, CREATE TABLE is one of the most fundamental and essential commands because it is used to define the structure of data before storing it. Without creating a table, we cannot insert, update, or retrieve any data. A database is an organized collection of related data. Inside a database, data is stored in tables. A table consists of rows and columns. Rows are called records and columns are called fields. Each column stores a specific type of information such as name, roll number, marks, salary, date, or address. Before inserting any data into a table, we must first define its structure. This structure includes the table name, column names, data types, and constraints. The CREATE TABLE command is used for this purpose. The basic syntax of the CREATE TABLE command is written as follows: CREATE TABLE table_name ( column1 datatype(size), column2 datatype(size), column3 datatype(size) ); In this syntax, table_name is the name of the table that you want to create. Inside the parentheses, you define column names along with their respective data types. Each column definition is separated by a comma. The command ends with a semicolon. For example, if we want to create a simple Student table, we can write: CREATE TABLE Student ( RollNo INT, Name VARCHAR(30), Marks INT ); In this example, Student is the table name. RollNo and Marks are integer data types, while Name is a variable-length character data type that can store up to 30 characters. After executing this command, an empty table structure will be created in the database. Understanding data types is very important in Class 11 Informatics Practices. Data types define the type of values that a column can store. INT is used to store whole numbers. VARCHAR is used to store text of variable length. CHAR is used to store fixed-length text. FLOAT is used to store decimal numbers. DATE is used to store date values. Choosing the correct data type is important because it ensures proper storage and data accuracy. Another important concept related to CREATE TABLE is constraints. Constraints are rules applied to columns to restrict the type of data that can be inserted. Constraints help maintain data integrity and prevent incorrect data entry. One of the most commonly used constraints is NOT NULL. When a column is defined as NOT NULL, it means that the column cannot store empty values. For example: CREATE TABLE Student ( RollNo INT NOT NULL, Name VARCHAR(30) NOT NULL, Marks INT ); Here, RollNo and Name must always contain values. They cannot be left blank. Another important constraint is PRIMARY KEY. A primary key uniquely identifies each record in a table. A primary key column cannot contain duplicate values and cannot contain NULL values. For example: CREATE TABLE Student ( RollNo INT PRIMARY KEY, Name VARCHAR(30), Marks INT ); In this case, RollNo is the primary key, and each student must have a unique roll number. The UNIQUE constraint is used to prevent duplicate values in a column. Unlike the primary key, a UNIQUE column can allow one NULL value depending on the database system. For example: CREATE TABLE Employee ( EmpID INT PRIMARY KEY, Email VARCHAR(50) UNIQUE ); In this example, no two employees can have the same email address. The DEFAULT constraint is used to assign a default value to a column if no value is provided during insertion. For example: CREATE TABLE Student ( RollNo INT PRIMARY KEY, Name VARCHAR(30), City VARCHAR(20) DEFAULT 'Delhi' ); If the city is not specified while inserting data, the value Delhi will automatically be stored. The CHECK constraint is used to apply a condition on a column. It ensures that all values in the column satisfy a specific.