ACID Properties with SQL Transactions in DBMS

🔍 Demystifying SQL Constraints with Oracle Live SQL

Lately, I’ve been exploring Oracle Live SQL, and it’s been an exciting deep dive into how constraints and transaction control maintain the accuracy and reliability of data. I thought I’d share a few takeaways from my learning journey — especially how constraints act as invisible guards for your database!

🧱 Understanding Why Constraints Matter

When you design a database, constraints are like the rules that keep your data honest.

They prevent invalid entries and ensure your tables stay consistent.

Here’s a simple example I practiced:

CREATE TABLE ACCOUNTS (
account_id NUMBER,
account_type VARCHAR2(20),
balance NUMBER,
CONSTRAINT acc_pk PRIMARY KEY (account_id),
CONSTRAINT acc_balance_ck CHECK (balance >= 0) -- No negative balances allowed!
);

This structure guarantees two important things:

Every account must have a unique identifier.

No one can insert a negative balance, ensuring clean and logical financial data.

💡 In short: Constraints keep your tables reliable even before a single line of application code is written.

⚙️ Playing with Transactions: Merge or Mayhem?

Next, I experimented with transactions to see how SQL behaves when duplicate or conflicting data is inserted.

This helped me understand how constraints interact with multiple inserts inside a single block.

BEGIN
INSERT INTO Accounts VALUES ('David', 3000);
INSERT INTO Accounts VALUES ('David', 4000);
END;

Depending on how your schema is designed, this block might:

Merge the balances intelligently (if logic is built to handle it), or

Throw an error for violating the unique or primary key constraint.

This experiment taught me that transactions are not just about committing data—they’re also about managing conflicts and maintaining data accuracy when something goes wrong.

🧠 The Power of Minimal Insert Testing

To better understand how constraints respond to incomplete data, I tried inserting a record without all the required fields:

INSERT INTO Accounts (acc_no, name)
VALUES (101, 'Pranav');

If your table enforces a NOT NULL constraint or a DEFAULT value for the balance column, the database will either:

Reject the record immediately (constraint violation), or

Automatically fill in the missing value with a default.

Either way, it’s a great way to test the strength and flexibility of your schema design.

🔒 Key Takeaways

Primary Key → Ensures every row is unique.

Check Constraint → Validates that your data follows logical rules.

Transactions → Help you handle multiple actions safely.

Testing Inserts → Reveals how well your design prevents bad data.

🚀 Final Thoughts

Working with Oracle Live SQL gave me a hands-on understanding of how small details—like a single constraint—can protect entire databases from corruption.

Whether you’re a beginner or brushing up on SQL fundamentals, playing around with constraints and transactions is one of the best ways to build intuition for data integrity.

Thanks @santhoshnc sir for his guidance and support.