📘 Selecting Data

Welcome to the Selecting Data module! This foundational learning path is designed to help you master the basics of querying data, particularly focusing on how to retrieve specific information from databases effectively.

📘 Creating SQL Table

In this tutorial, you'll learn how to interpret and use rows in a database table. Tables are essential to storing structured data, and each row in a table represents a unique item or record.

Each row of a table represents a new item.

Each column of a table represents a specific attribute of the data, such as id, name, or username. These columns define the type of information stored for each item in the table.

For example, consider a table named Friends. Below is how a simple table might look:

info

SQL Table

Friends

| id | name            | username         |
|----|-----------------|------------------|
| 1  | John Doe        | @johndoe         |
| 2  | Jane Smith      | @janesmith       |
| 3  | Bob Johnson     | @bobjohnson      |

SQL Code

Creating SQL Tables & db.

-- creating database
CREATE DATABASE my_database;

-- use the database you created
USE my_database;


-- Create the table
CREATE TABLE friends (
id INT PRIMARY KEY,
name VARCHAR(100),
username VARCHAR(100)
);

-- Insert data into the table
INSERT INTO friends (id, name, username) VALUES
(1, 'John Doe', '@johndoe'),
(2, 'Jane Smith', '@janesmith'),
(3, 'Bob Johnson', '@bobjohnson');

Output

id	name	username
1	John Doe	@johndoe
2	Jane Smith	@janesmith
3	Bob Johnson	@bobjohnson

🧾 Explanation

The first row of this table contains:

• id: 1
• name: John Doe
• username: @johndoe

Each of the remaining rows represents a different friend, with unique ID, name, and username values.

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✅ This is your first step in understanding how data is structured in relational databases. Once you master rows, you're on your way to writing powerful SQL queries!

📘 Querying a Table with FROM

To query data from a table, use the FROM clause followed by the table's name.

For example, consider a table named Friends. Below is how a simple table might look:

info

SQL Table

Friends

| id | name              | email                   |
|----|-------------------|--------------------------|
| 1  | Tony Stark        | ironman@avengers.com     |
| 2  | Bruce Wayne       | batman@gotham.com        |
| 3  | Leia Organa       | princess@rebellion.org   |

SQL Code

Creating SQL Tables.

SELECT name
FROM friends;

Output

id	name	email
1	Tony Stark	ironman@avengers.com
2	Bruce Wayne	batman@gotham.com
3	Leia Organa	princess@rebellion.org

tip

When requesting data with SQL staments like SELECT, we say that we are making a query. From helps in select the name col from While not necessary but its a good practice to finish the sql queries with;

By following these best practices,

🔄 Selecting Multiple Columns in SQL

info

SQL Table

friends

| id | name              | email                   |
|----|-------------------|--------------------------|
| 1  | Tony Stark        | ironman@avengers.com     |
| 2  | Bruce Wayne       | batman@gotham.com        |
| 3  | Leia Organa       | princess@rebellion.org   |

SQL Code

Creating SQL Tables.

SELECT name, email
FROM friends;

Output

name	email
Tony Stark	ironman@avengers.com
Bruce Wayne	batman@gotham.com
Leia Organa	princess@rebellion.org

🧹 Selecting Unique Values with DISTINCT

Sometimes your table might contain duplicate values, and you only want to see each unique value once in your result.

That’s where the DISTINCT keyword comes in!

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info

SQL Table

Subscribers

| name | email             | country  |
|------|-------------------|----------|
| Sam  | sam17@mail.com    | England  |
| Remy | rem@mail.com      | France   |
| Luis | luis_99@mail.com  | France   |

SQL Code

Creating SQL Tables.

SELECT DISTINCT country
FROM subscribers;

Output

country
England
France

✅ What You have Learned

This module covers four essential topics in data selection:

• Rows and Columns
  Learn how to access specific rows and columns in a dataset or table, the building blocks of any query.

• Select Data
  Understand the basic SELECT statement to retrieve data from a database.

• Select Multiple Columns
  Retrieve more than one column at a time in your queries to get the information you need all at once.

• Select Distinct Values
  Use DISTINCT to eliminate duplicate records and identify unique entries within your dataset.

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