SELECT Basics

The SELECT Statement

The SELECT statement is the most used SQL command. It retrieves data from one or more tables.

Selecting Specific Columns

Instead of SELECT * (all columns), you can name exactly which columns you want:

SELECT name, price FROM products;

This is better practice than SELECT * because:

• You get only the data you need
• Queries are faster — less data to transfer
• Your code doesn't break if new columns are added

Column Aliases with AS

Use AS to rename a column in the result:

SELECT name AS product_name, price AS cost
FROM products;

Aliases are useful for:

• Making output more readable
• Renaming calculated expressions
• Shortening long column names

DISTINCT — Removing Duplicates

SELECT DISTINCT returns unique values only:

SELECT DISTINCT category FROM products;

Without DISTINCT, every row in the table is returned even if it has the same category as another row. With DISTINCT, each unique category appears once.

Expressions and Calculations

You can compute values directly in SELECT:

SELECT
  name,
  price,
  price * 1.08 AS price_with_tax
FROM products;

MySQL supports all arithmetic operators: +, -, *, /, % (modulo).

String Literals

You can include constant text in results:

SELECT name, 'in stock' AS availability
FROM products;

The Order of Clauses

In a full SELECT statement, clauses must appear in this order:

SELECT   column1, column2
FROM     table_name
WHERE    condition
GROUP BY column
HAVING   group_condition
ORDER BY column
LIMIT    n;

You will learn each clause in upcoming lessons. For now, focus on SELECT and FROM.

Your Task

Use SELECT DISTINCT to find all unique product categories. Return only the category column.