Day 1: Your First SQL Query — SELECT, FROM, WHERE

What You'll Build Today

A set of working queries against a real sales database — find top customers, filter orders by date range, sort products by revenue. By the end, SQL will feel like asking questions in English.

Setup

Installing SQLite and a GUI

SQLite runs entirely on your laptop — no server, no account, no configuration. It's used inside every iPhone, Android, and most desktop applications. Perfect for learning.

Download DB Browser for SQLite from sqlitebrowser.org. It's free and gives you a visual interface. Install it, then open it.

Now grab the practice database. Create a file called sales.db — we'll populate it with this SQL:

sql setup.sql

CREATE TABLE customers (
  id      INTEGER PRIMARY KEY,
  name    TEXT,
  city    TEXT,
  segment TEXT
);

CREATE TABLE orders (
  id          INTEGER PRIMARY KEY,
  customer_id INTEGER,
  order_date  TEXT,
  amount      REAL,
  status      TEXT
);

INSERT INTO customers VALUES
  (1,'Acme Corp','Denver','Enterprise'),
  (2,'BetaCo','Austin','SMB'),
  (3,'Gamma LLC','New York','Enterprise'),
  (4,'Delta Inc','Chicago','SMB'),
  (5,'Epsilon','Denver','Startup');

INSERT INTO orders VALUES
  (1,1,'2025-01-15',12500.00,'completed'),
  (2,2,'2025-01-22',3200.00,'completed'),
  (3,1,'2025-02-08',8900.00,'completed'),
  (4,3,'2025-02-14',21000.00,'completed'),
  (5,4,'2025-03-01',1500.00,'pending'),
  (6,5,'2025-03-10',4700.00,'completed');

In DB Browser: click Open Database → create a new file → paste that SQL into the Execute SQL tab → click Run. You now have a real database with real data.

Core Concept

SELECT and FROM — Reading Data

Every SQL query you'll ever write starts with SELECT (what columns you want) and FROM (which table). That's it.

sql

-- Get every column from customers
SELECT * FROM customers;

-- Get only the name and city columns
SELECT name, city FROM customers;

-- Rename a column in the output with AS
SELECT name AS customer_name, city AS location
FROM customers;

The * means "all columns." It's fine for exploring — in production code, always name your columns explicitly so you know exactly what you're getting.

Filtering

WHERE — Filtering Rows

WHERE filters which rows come back. It's the most powerful clause in basic SQL — think of it as the filter in a spreadsheet, but with full logical operators.

sql

-- Customers in Denver only
SELECT * FROM customers
WHERE city = 'Denver';

-- Orders over $5,000
SELECT * FROM orders
WHERE amount > 5000;

-- Completed orders over $5,000 (AND = both conditions)
SELECT * FROM orders
WHERE status = 'completed'
  AND amount > 5000;

-- Orders from Denver OR Chicago customers (OR = either)
SELECT * FROM customers
WHERE city = 'Denver' OR city = 'Chicago';

-- Shorthand for OR on the same column: IN
SELECT * FROM customers
WHERE city IN ('Denver', 'Chicago');

-- Orders in a date range (dates stored as text, comparison still works)
SELECT * FROM orders
WHERE order_date BETWEEN '2025-01-01' AND '2025-02-28';

Text comparisons are case-sensitive in SQLite. 'Denver' and 'denver' are different values. Use LOWER(city) = 'denver' if your data is inconsistent.

Sorting and Limiting

ORDER BY and LIMIT

Sort your results and limit how many rows come back. Essential for "show me the top 10" queries.

sql

-- Orders sorted largest to smallest
SELECT * FROM orders
ORDER BY amount DESC;

-- Top 3 orders by amount
SELECT * FROM orders
ORDER BY amount DESC
LIMIT 3;

-- Customers sorted alphabetically
SELECT name, city FROM customers
ORDER BY name ASC;

-- Most recent completed orders, top 5
SELECT id, order_date, amount FROM orders
WHERE status = 'completed'
ORDER BY order_date DESC
LIMIT 5;

SQL clause order matters: SELECT → FROM → WHERE → ORDER BY → LIMIT. You can't put LIMIT before WHERE. The database executes them in a specific order even if you could write them differently.

Practice Challenges

Test what you just learned

Write a query returning all Enterprise customers.
Find all orders with amount between $3,000 and $15,000.
Return the 2 largest completed orders, showing only order_date and amount.
List all customers NOT in Denver. (Hint: != or <> means "not equal")

Day 1 Complete — What You Learned

SET UP SQLite and DB Browser for SQLite
SELECT columns with FROM — the foundation of every query
Filter rows with WHERE, AND, OR, IN, BETWEEN
Sort results with ORDER BY ASC / DESC
Limit result count with LIMIT

Course progress

20%

Day 1 Done

Tomorrow: JOINs and aggregations

Day 2 is where SQL gets powerful — combining tables and calculating totals, averages, and counts across real data.

Day 2: JOINs and GROUP BY

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