Beginner4 lessons

Filtering & Logic

Stop returning too many rows. Master WHERE clauses with AND, OR, LIKE, IN, BETWEEN, and NULL handling — the difference between a query that works and one that almost works.

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Lessons · 4 total

AND, OR, NOT

Combine multiple conditions in a WHERE clause.

→2

IN, BETWEEN, LIKE

Range and pattern matching.

→3

Working with NULL

NULL is "unknown" — comparisons need IS NULL.

→4

EXISTS — test for related rows

Apply EXISTS and advanced filtering patterns to test related data without overcomplicating joins. This lesson improves query intent and helps you avoid false positives in relationship checks.

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The WHERE clause is where most queries succeed or fail. This course teaches you to write predicates that return exactly the rows you mean — no more, no less.

What you'll learn

Combine conditions with AND, OR, and NOT
Match a list of values with IN and NOT IN
Check numeric or date ranges with BETWEEN
Pattern-match text with LIKE (% wildcard) and ILIKE (case-insensitive)
Handle missing data correctly with IS NULL and IS NOT NULL
Control evaluation order with parentheses (why AND binds tighter than OR)

What you'll practice on

The HR database and the Store database. You'll filter employees by salary range and hire date, find customers by name pattern, and write conditions that correctly handle rows where data is missing.

Prerequisites

SQL Fundamentals (or equivalent — you should know SELECT, FROM, and basic WHERE).