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Intermediate Topic 24 of 51 Databases

Transactions

Groups of operations executed as an atomic unit.

How it works

A transaction groups several database operations into a single logical unit of work that either completes entirely or has no effect. Applications start it, run statements and then COMMIT to make changes permanent or ROLLBACK to undo them. The database ensures atomicity, consistency, isolation and durability, using logs and locking or multi-version techniques. Savepoints allow partial rollbacks.

Step-by-step walkthrough

  1. BEGIN starts a transaction.
  2. Debit 100 from account A.
  3. Credit 100 to account B.
  4. COMMIT makes both changes permanent together.
  5. On any error ROLLBACK undoes both.

Where it is used

Transferring money between accounts, placing an order that reduces stock and inserts lines, and any multi-step update that must not be left half-done use transactions.

Common pitfall

Long-running transactions hold locks, block others and bloat logs or version storage. Forgetting to commit or roll back leaves connections idle in transaction. Assuming that two separate statements are atomic without a transaction causes races. Keep transactions short, handle deadlock and serialization failures by retrying and avoid user interaction inside them.

Where it fits in the course

Transactions is topic 24 of 51 in Databases, rated Intermediate. It follows Denormalization. The next topic is ACID Properties.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Databases quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Transactions?
Groups of operations executed as an atomic unit. It belongs to Databases and is an intermediate-level topic.
Where do people use Transactions?
Transferring money between accounts, placing an order that reduces stock and inserts lines, and any multi-step update that must not be left half-done use transactions.
What is the most common mistake with Transactions?
Long-running transactions hold locks, block others and bloat logs or version storage.
What should I learn before this topic?
Start with Denormalization, the topic just before it in Databases.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Databases quiz.
Is Transactions hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Transactions?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Transactions?
Denormalization, ACID Properties, Normal Forms are closely connected. The full list is in the related topics section of this page.
What should I study after Transactions?
Continue with ACID Properties, the next topic in Databases.

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