Last year in college , I had the opportunity to dive deep into SQL. The course was made even more exciting by an amazing instructor . Fast forward to today, and I regularly use SQL in my backend development work with PHP. Today, I felt the need to refresh my SQL knowledge a bit, and that's why I've put together three posts aimed at helping beginners grasp the fundamentals of SQL.

Understanding Relational Databases

Let's Begin with the Basics: What Is a Database?

Simply put, a database is like a digital warehouse where you store large amounts of data. When you work on projects that involve data, you need a place to keep that data organized and accessible, and that's where databases come into play.

Exploring Different Types of Databases

When it comes to databases, there are two primary types to consider: relational and non-relational.

Relational Databases: Structured Like Tables

Think of a relational database as a collection of neatly organized tables, somewhat like rows and columns in an Excel spreadsheet. Each table represents a specific type of information, and these tables are interconnected through shared attributes. It's similar to a well-organized library catalog where you can find books by author, title, or genre.

Key Points:

Tables with rows and columns.

Data is neatly structured, much like a library catalog.

You use a structured query language (SQL) to interact with it.

Ideal for handling structured data with complex relationships.

Non-Relational Databases: Flexibility in Containers

Now, imagine a non-relational database as a collection of flexible containers, more like bins or boxes. Each container holds data, but they don't have to adhere to a fixed format. It's like managing a diverse collection of items in various boxes without strict rules. This flexibility is incredibly useful when dealing with unstructured or rapidly changing data, like social media posts or sensor readings.

Key Points:

Data can be stored in diverse formats.

There's no rigid structure; adaptability is the name of the game.

Non-relational databases (often called NoSQL databases) are commonly used.

Ideal for handling unstructured or dynamic data.

Now, Let's Dive into SQL:

SQL is a :

Data Definition language ( what todays post is all about )

Data Manipulation language

Data Query language

Task: Building and Interacting with a Bookstore Database

Setting Up the Database

Our first step in creating a bookstore database is to establish it. You can achieve this with a straightforward SQL command:

CREATE DATABASE bookstoreDB;

SQL Data Definition

As the name suggests, this step is all about defining your tables. By the end of this phase, your database and the tables within it are created and ready for action.

1 - Introducing the 'Books' Table

A bookstore is all about its collection of books, so our 'bookstoreDB' needs a place to store them. We'll call this place the 'books' table. Here's how you create it:

CREATE TABLE books ( -- Don't worry, we'll fill this in soon! );

Now, each book has its own set of unique details, including titles, authors, genres, publication years, and prices. These details will become the columns in our 'books' table, ensuring that every book can be fully described.

Now that we have the plan, let's create our 'books' table with all these attributes:

CREATE TABLE books ( title VARCHAR(40), author VARCHAR(40), genre VARCHAR(40), publishedYear DATE, price INT(10) );

With this structure in place, our bookstore database is ready to house a world of books.

2 - Making Changes to the Table

Sometimes, you might need to modify a table you've created in your database. Whether it's correcting an error during table creation, renaming the table, or adding/removing columns, these changes are made using the 'ALTER TABLE' command.

For instance, if you want to rename your 'books' table:

ALTER TABLE books RENAME TO books_table;

If you want to add a new column:

ALTER TABLE books ADD COLUMN description VARCHAR(100);

Or, if you need to delete a column:

ALTER TABLE books DROP COLUMN title;

3 - Dropping the Table

Finally, if you ever want to remove a table you've created in your database, you can do so using the 'DROP TABLE' command:

DROP TABLE books;

To keep this post concise, our next post will delve into the second step, which involves data manipulation. Once our bookstore database is up and running with its tables, we'll explore how to modify and enrich it with new information and data. Stay tuned ...

SQL is a short form of structured query language, and is sometimes referred to as S-Q-L or sometimes as See-Quell. This language is primarily designed to store data in related database management systems. It is a special tool used by professionals to manage structured data (data stored in the form of tables). You can easily create and manage a database, access and modify table rows and columns,…

In our previous database exploration journey, SQL Fundamentals #1: SQL Data Definition, we set the stage by introducing the "books" table nestled within our bookstore database. Currently, our table is empty, Looking like :

books

| title | author | genre | publishedYear | price |

Data manipulation

Now, let's embark on database interaction—data manipulation. This is where the magic happens, where our "books" table comes to life, and we finish our mission of data storage.

Inserting Data

Our initial task revolves around adding a collection of books into our "books" table. we want to add the book "The Great Gatsby" to our collection, authored F. Scott Fitzgerald. Here's how we express this in SQL:

INSERT INTO books(title, author, genre, publishedYear, price) VALUES('The Great Gatsby', 'F. Scott Fitzgerald', 'Classic', 1925, 10.99);

Alternatively, you can use a shorter form for inserting values, but be cautious as it relies on the order of columns in your table:

INSERT INTO books VALUES('The Great Gatsby', 'F. Scott Fitzgerald', 'Classic', 1925, 10.99);

Updating data

As time goes on, you might find the need to modify existing data in our "books" table. To accomplish this, we use the UPDATE command.For example :

UPDATE books SET price = 12.99 WHERE title = 'The Great Gatsby';

This SQL statement will locate the row with the title "The Great Gatsby" and modify its price to $12.99.

We'll discuss the where clause in (SQL fundamentals #3)

Deleting data

Sometimes, data becomes obsolete or irrelevant, and it's essential to remove it from our table. The DELETE FROM command allows us to delete entire rows from our table.For example :

DELETE FROM books WHERE title = 'Moby-Dick';

This SQL statement will find the row with the title "Moby-Dick" and remove it entirely from your "books" table.

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