📗 The Inequality Operator
The inequality operator (<> or !=) helps you find records that don't match a specific value. Think of it as asking "show me everything except this!"
Let's start with a simple example. Imagine you have a students table and want to find all students who are NOT in their first year:
- SQL Table
- SQL Code
- Output
| name | year | major |
|-------------|------|---------|
| Ava Smith | 1 | Biology |
| Luis Garcia | 1 | Physics |
| Lin Wong | 3 | Biology |
SELECT *
FROM students
WHERE year <> 1;
| name | year | major |
|---|---|---|
| Lin Wong | 3 | Biology |
📘 Let's Practice Together
Here's another way to look at it: the FROM clause tells SQL which table to look in, and WHERE tells it what to filter.
For example, consider a table named students. Let's see the same example again to reinforce the concept:
- SQL Table
- SQL Code
- Output
| name | year | major |
|-------------|------|---------|
| Ava Smith | 1 | Biology |
| Luis Garcia | 1 | Physics |
| Lin Wong | 3 | Biology |
SELECT *
FROM students
WHERE year <> 1;
| name | year | major |
|---|---|---|
| Lin Wong | 3 | Biology |
The inequality operator is your "everything except" tool! It's perfect when you want to exclude specific values from your results.
What it works with:
- Numbers:
age <> 25(everyone except 25-year-olds) - Text:
major <> 'Biology'(all majors except Biology) - Dates:
signup_date <> '2024-01-01'(all dates except New Year's Day)
Pro tip: Use this when you know what you DON'T want in your results!
🔄 More Powerful Comparisons
The Problem: Sometimes you need more than just "equal" or "not equal."
Real-world scenario: You're analyzing air quality data and want to find cities with low pollution levels (under 100 on the pollution index).
Good to know:
- Numbers don't need quotes:
pollution_index < 100✅- Text needs quotes:
city = 'Tokyo'✅- The
<symbol means "less than" - just like in math!
Here's how to find cities with clean air (pollution index under 100):
- SQL Table
- SQL Code
- Output
| city | pollution_index |
|----------|-----------------|
| Delhi | 168 |
| Milano | 122 |
| Shanghai | 74 |
| Tokyo | 21 |
SELECT *
FROM pollution
WHERE pollution_index < 100;
| city | pollution_index |
|---|---|
| Shanghai | 74 |
| Tokyo | 21 |
🧹 Including the Boundary Value
What if we want cities with "acceptable" pollution levels? Let's say anything 122 or below is acceptable.
The <= operator means "less than or equal to" - it includes the exact value too!
- SQL Table
- SQL Code
- Output
| city | pollution_index |
|----------|-----------------|
| Delhi | 168 |
| Milano | 122 |
| Shanghai | 74 |
| Tokyo | 21 |
SELECT *
FROM pollution
WHERE pollution_index <= 122;
| city | pollution_index |
|---|---|
| Milano | 122 |
| Shanghai | 74 |
| Tokyo | 21 |
🎯 Getting Only What You Need
Smart tip: You don't always need all the data! Sometimes you only want specific columns to make your results cleaner and easier to read.
Example: Instead of seeing all student info, maybe you just want names and years.
Memory trick: Think of
SELECT *as "give me everything" andSELECT name, yearas "just give me the basics"
- SQL Table
- SQL Code
- Output
| name | year | major |
|-------------|------|---------|
| Ava Smith | 1 | Biology |
| Luis Garcia | 1 | Physics |
| Lin Wong | 3 | Biology |
SELECT name, year
FROM students
WHERE year = 1;
| name | year |
|---|---|
| Ava Smith | 1 |
| Luis Garcia | 1 |
🎉 What You've Mastered
Great job! You've learned the essential skills for smart data filtering:
🚫 The "Not Equal" Expert
You can now use <> and != to exclude specific values and find everything except what you don't want.
📊 The Comparison Pro
You've mastered <, >, <=, and >= for finding records above, below, or within specific ranges.
🎯 The Precision Selector
You know how to pick just the columns you need instead of grabbing everything with *.
🔍 The Smart Filterer
You can combine WHERE clauses with any operator to create laser-focused queries that find exactly what you're looking for.
Next up: Try combining these operators with AND and OR to create even more powerful searches!