Filtering, Sorting, and Limiting Results

What do WHERE and ORDER BY do?

Row-limiting syntax differs by system:

Example

SELECT order_id, total_amount
FROM orders
WHERE total_amount >= 1000
ORDER BY total_amount DESC
LIMIT 10;

How it works

1. Reads the orders table
2. Keeps orders worth at least 1,000
3. Sorts them highest first
4. Returns the first ten rows

• Use single quotes around text values: WHERE region = 'South'
• Use date literals in a standard format: WHERE order_date >= '2026-07-01'

Useful conditions

Common mistakes

• NULL is not zero or an empty string. It means "unknown".
  • ✅ WHERE email IS NULL
  • ❌ WHERE email = NULL (never true)
• Mixing AND and OR without parentheses:
  • ❌ WHERE region = 'South' OR region = 'East' AND total_amount > 500
  • ✅ WHERE (region = 'South' OR region = 'East') AND total_amount > 500
  • AND is evaluated before OR, so the first version doesn't do what it looks like.
• BETWEEN with timestamps: BETWEEN '2026-07-01' AND '2026-07-31' may miss events on 31 July after midnight. Use >= '2026-07-01' AND < '2026-08-01' instead.

Try it: Find orders from the South region with amounts above 500, sorted from newest to oldest.