Creating Database Tables in SQL

Creating Database Tables in SQL: Comprehensive Guide

Creating and managing database tables in SQL involves several key operations: CREATE, UPDATE, DELETE, ALTER, and DROP. This section of the guide will explore each of these commands, focusing on syntax, best practices, the use of primary keys and foreign keys, and the application of constraints to ensure data integrity and optimize database performance.

Table Creation: Syntax

The CREATE TABLE statement is used to create a new table in the database. It is one of the most fundamental SQL commands, essential for defining the structure of your data.

Syntax

CREATE TABLE table_name (
    column1 datatype constraints,
    column2 datatype constraints,
    ...
    columnN datatype constraints,
    PRIMARY KEY(one or more columns),
    FOREIGN KEY(one or more columns) REFERENCES other_table(columns),
    ...
);

Example

CREATE TABLE Employees (
    EmployeeID int NOT NULL,
    FirstName varchar(255) NOT NULL,
    LastName varchar(255),
    Email varchar(255),
    DepartmentID int,
    PRIMARY KEY (EmployeeID),
    FOREIGN KEY (DepartmentID) REFERENCES Departments(DepartmentID)
);

Code Explanation

• EmployeeID is an integer and marked as NOT NULL, meaning every record must have a unique employee ID.
• FirstName and LastName are variable character strings, with FirstName required.
• Email is an optional variable character string field.
• DepartmentID is a foreign key that links to the Departments table, establishing a relationship between each employee and their respective department.