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Beginner 16 min readModule: Module 4: Querying Data with SELECT, WHERE & ORDER BY

Advanced WHERE Filters, Pattern Matching & Pagination

Filter datasets using pattern matching (LIKE/ILIKE), NULL safety (IS NOT NULL), and implement OFFSET/LIMIT pagination.

What You Will Learn in This Lesson

  • Pattern matching with LIKE '%text%' and case-insensitive ILIKE
  • Handling three-valued logic with IS NULL and IS NOT NULL
  • Keyset cursor pagination vs OFFSET/LIMIT pagination

Introduction & Core Concept

The SELECT statement retrieves rows matching precise filtering criteria and sorts them in ascending (ASC) or descending (DESC) order.
WHY DOES THIS MATTER IN THE REAL WORLD?

In SQL, NULL = NULL is UNKNOWN (not true). You must use IS NULL to test for missing values.

Filtered Search with Pagination

sql
sql
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SELECT id, name, email, score
FROM students
WHERE email ILIKE '%@kwasacademy.dev'
  AND score BETWEEN 80 AND 100
  AND status IS NOT NULL
ORDER BY score DESC
LIMIT 10 OFFSET 0;

Line-by-Line Technical Breakdown

1High OFFSET values (e.g. OFFSET 100000) are slow; use cursor pagination on large tables.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[SQL]
SQL SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Use keyset cursor pagination (WHERE id > last_seen_id) for large datasets.

Lesson Summary & Core Takeaways

  • SELECT and WHERE clauses extract precise subsets of data efficiently.