SQL Queries Every Developer Should Know

Source: Dev.to

Introduction to SQL

If you are a web developer, chances are you have worked with a database at some point. It might be PostgreSQL, MySQL, SQLite, or something else. No matter the stack, SQL is always there behind the scenes. And let’s be honest, few things feel better than writing a single SQL query that returns exactly the data you need. Extra points if it runs fast. In this article, we’ll walk through essential SQL queries every developer should know. Whether you are building APIs, dashboards, or debugging a production issue at 2 AM, these queries are your daily tools.

SELECT – The Foundation

If SQL were a movie, SELECT would be the origin story. Every meaningful query starts here.

Use SELECT to fetch only the data you actually need. While SELECT * looks convenient, it can slow down queries and waste bandwidth, especially on large tables.

The real power of SELECT comes when you combine it with WHERE, JOIN, and ORDER BY.

SELECT id, name, email
FROM users;

WHERE – Filtering the Noise

Databases can store millions of rows. WHERE helps you narrow things down to what actually matters.

You can filter using:

• Comparison operators: =, !=, =
• Logical operators: AND, OR, NOT

Without WHERE, things can get dangerous. A query like DELETE FROM users; without a condition will delete everything. Always double‑check.

SELECT *
FROM orders
WHERE status = 'completed';

INSERT – Adding New Data

Whenever a user signs up, places an order, or uploads something, you’ll need INSERT.

Best practices

• Always specify column names.
• Use bulk inserts when possible for better performance.
• Never trust user input. Use parameterized queries or an ORM to prevent SQL injection.

INSERT INTO users (name, email)
VALUES ('Alice', 'alice@example.com');

UPDATE – Changing Existing Data

Emails change, addresses change, and bugs happen. That’s where UPDATE comes in.

The most common and most dangerous mistake is forgetting the WHERE clause. Without it, every row gets updated.

Tips

• You can update multiple columns at once.
• Use transactions in production to stay safe.

UPDATE users
SET email = 'alice@newdomain.com'
WHERE id = 42;

DELETE – Removing Data

When it’s time to clean up old or unused data, DELETE does the job.

Use cases

• Removing expired sessions
• Cleaning test data
• Deleting old logs

Many production apps use soft deletes by adding a deleted_at column instead of permanently removing records.

DELETE FROM sessions
WHERE last_active  100
);

Final Thoughts

Mastering these queries will help you:

• Debug faster by querying the database directly
• Build better and faster APIs
• Write cleaner backend logic
• Impress teammates during code reviews

SQL is not scary. It’s a superpower. And like any skill, the more you practice it, the more confident and unstoppable you become.