SELECT Basics

Reading Data

SELECT is the most used SQL statement. It asks the database for rows and columns.

SELECT name, email FROM customers;
SELECT * FROM customers;             -- every column
SELECT 1 + 1;                        -- expressions work too
SELECT DISTINCT city FROM customers; -- unique values only

Aliases Make Output Readable

SELECT name AS customer_name, city AS hometown FROM customers;

The AS keyword renames a column in the result set. Some databases allow omitting AS, but writing it is clearer.

Sorting Results

SELECT name, city FROM customers ORDER BY name ASC;
SELECT name, city FROM customers ORDER BY city DESC, name ASC;

ORDER BY sorts. ASC (ascending, A-Z) is the default; DESC reverses it. You can sort by several columns, applied left to right.

Limiting How Many Rows Come Back

• MySQL / PostgreSQL / SQLite: LIMIT 10 OFFSET 20.
• SQL Server: SELECT TOP 10 ... or OFFSET/FETCH.
• Oracle (12c+): OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY.

A Tiny Example

SELECT id, name, city
FROM customers
WHERE is_active = 1
ORDER BY created_at DESC
LIMIT 5;

Key Points

• SELECT picks columns, FROM names the table.
• ORDER BY sorts; DISTINCT deduplicates; LIMIT pages.
• Aliases with AS rename output columns.
• Dialects differ slightly on limiting rows.