Your First SELECT Query

The SELECT statement is the workhorse of SQL. It's how you retrieve data from a database — and you'll use it in virtually every query you write.

Basic Syntax

SELECT column1, column2
FROM table_name;

Let's break it down:

• SELECT — tells the database what columns you want
• FROM — tells the database which table to look in

Selecting All Columns

Use * (asterisk) to select every column:

SELECT * FROM users;

Result:

id | name           | email                | created_at
---+----------------+---------------------+------------
1  | Alice Johnson  | alice@example.com   | 2024-01-15
2  | Bob Smith      | bob@example.com     | 2024-01-16
3  | Carol White    | carol@example.com   | 2024-01-17
...

Tip: In production, avoid SELECT * — always specify the columns you need. It's faster and less fragile.

Selecting Specific Columns

SELECT name, email FROM users;

Result:

name           | email
---------------+---------------------
Alice Johnson  | alice@example.com
Bob Smith      | bob@example.com
Carol White    | carol@example.com

Aliasing Columns with AS

You can rename columns in the output using AS:

SELECT
  name AS customer_name,
  email AS contact_email
FROM users;

Result:

customer_name  | contact_email
---------------+---------------------
Alice Johnson  | alice@example.com
Bob Smith      | bob@example.com

Aliases are especially useful when column names are long, ambiguous, or when using calculated values.

Calculated Columns

SQL can do math inline:

SELECT
  name,
  price,
  price * 1.1 AS price_with_tax
FROM products;

Result:

name                | price   | price_with_tax
--------------------+---------+---------------
Laptop Pro 15"      | 1299.99 | 1429.989
Mechanical Keyboard | 89.99   | 98.989
USB-C Hub           | 39.99   | 43.989

String Concatenation

Combine text values (syntax varies by database):

-- SQLite / most databases
SELECT
  id,
  name || ' <' || email || '>' AS contact
FROM users;

-- PostgreSQL also supports ||
-- MySQL uses CONCAT()

Result:

id | contact
---+------------------------------------------
1  | Alice Johnson <alice@example.com>
2  | Bob Smith <bob@example.com>

DISTINCT — Remove Duplicates

Use DISTINCT to get unique values only:

SELECT DISTINCT category FROM products;

Result:

category
----------
Electronics
Office
Furniture

Without DISTINCT, if multiple products share a category, that category would appear multiple times.

LIMIT — Control Result Size

Restrict how many rows are returned:

SELECT * FROM products LIMIT 3;