Learning SQL After Using MongoDB

· 2 min read
sqldatabasespostgresql

After using MongoDB for over a year, I’m now learning SQL databases (specifically PostgreSQL).

Why I’m Learning SQL

  • Most companies use SQL databases
  • Some data fits better in relational databases
  • SQL is a fundamental skill
  • I want to understand when to use SQL vs NoSQL

First Impressions

Tables feel rigid: Coming from MongoDB’s flexible documents, SQL tables feel strict.

Relationships are explicit: Foreign keys and joins are built into the design.

SQL syntax is different: It’s not JavaScript, it’s its own language.

Basic SQL I’m Learning

Creating tables:

CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  email VARCHAR(100) UNIQUE NOT NULL,
  created_at TIMESTAMP DEFAULT NOW()
);

Inserting data:

INSERT INTO users (name, email)
VALUES ('John Doe', 'john@example.com');

Querying data:

SELECT * FROM users WHERE email = 'john@example.com';

Updating data:

UPDATE users SET name = 'Jane Doe' WHERE id = 1;

Deleting data:

DELETE FROM users WHERE id = 1;

Understanding Relationships

One-to-many:

CREATE TABLE posts (
  id SERIAL PRIMARY KEY,
  title VARCHAR(200),
  user_id INTEGER REFERENCES users(id)
);

Joins:

SELECT users.name, posts.title
FROM users
JOIN posts ON users.id = posts.user_id;

What’s Different from MongoDB

Schema is required: I have to define the structure upfront.

Relationships are explicit: Foreign keys enforce data integrity.

Joins are powerful: Combining data from multiple tables is built-in.

Transactions: ACID properties ensure data consistency.

What I’m Struggling With

Complex joins: Joining multiple tables gets confusing.

Normalization: Understanding when to split data into multiple tables.

SQL syntax: It’s verbose compared to MongoDB queries.

Migrations: Changing the schema in production is tricky.

When to Use SQL vs MongoDB

I’m learning:

Use SQL when:

  • Data has clear relationships
  • Data integrity is crucial
  • Complex queries are common
  • Schema is stable

Use MongoDB when:

  • Schema is flexible or evolving
  • Data is hierarchical
  • Rapid prototyping
  • Horizontal scaling is needed

What I’m Building

To practice SQL, I’m building:

  • A blog with users, posts, and comments
  • An e-commerce database with products, orders, and customers
  • Converting some MongoDB projects to PostgreSQL

Resources I’m Using

  • PostgreSQL documentation
  • SQL tutorials on YouTube
  • SQLBolt (interactive SQL tutorial)
  • Building projects

Current Understanding

SQL databases aren’t “old” or “outdated” they’re still the best choice for many applications.

MongoDB and SQL solve different problems. Understanding both makes me a better developer.

I’m glad I’m learning SQL. It’s opening my eyes to different ways of thinking about data.

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