🌱BeginnerData Manipulation
SELECT Statement
Retrieve data from tables using SELECT, choosing specific columns and all rows.
Overview
SELECT is the most-used SQL statement. It retrieves rows and columns from one or more tables. At its simplest, SELECT * FROM table returns every column and every row. In practice, always name the specific columns you want SELECT * is convenient but fragile; schema changes can break applications and return unnecessary data.
SELECT can also compute values inline you can do arithmetic, call functions, and combine string expressions without any table at all: SELECT 1 + 1 or SELECT NOW() work fine. This makes SELECT a general-purpose expression evaluator as well as a data retrieval tool.
The full SELECT clause order is: SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY → LIMIT. Understanding this clause order and the logical processing sequence helps write correct queries.
Key Points
- •SELECT col1, col2 FROM table retrieves specific columns
- •SELECT * FROM table retrieves all columns (avoid in production code)
- •SELECT without FROM evaluates expressions: SELECT 1+1, NOW()
- •Column aliases: SELECT price * 1.1 AS price_with_tax
- •Clause order: SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY → LIMIT
Examples
Basic SELECT patterns
-- All columns
SELECT * FROM products;
-- Specific columns only
SELECT id, name, price FROM products;
-- With expressions and alias
SELECT
name,
price,
price * 1.2 AS price_with_vat
FROM products;SELECT without a table
SELECT 42 AS answer;
SELECT NOW() AS current_time;
SELECT UPPER('hello') AS greeting;
SELECT 10 / 3 AS integer_division, 10.0 / 3 AS real_division;Exercises
Write SQL to solve each exercise. Your progress is saved automatically.
Loading editor…
Completed: 0 / 5 exercises
Knowledge Check
Question 1 of 4