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Hectal
Roadmap
Phase 7Beginner10 of 19 in the curriculum

Database Fundamentals

Tables, ACID, isolation levels, indexes, joins, normalization.

Before scaling a database you have to be fluent with one. This phase covers the SQL core: schema design, transactions, and — the thing interviews actually probe — how indexes decide whether your query is 1ms or 10s.

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7 topics ~47 min 8 code blocks & diagrams
Start with the first topic
1
7.1

SQL Basics

Tables, primary/foreign keys, indexes, constraints — the vocabulary of relational modeling.

7 min 1 code practice

2
7.2

Transactions / ACID

Atomicity, Consistency, Isolation, Durability — the contract that makes bank transfers safe and your LLD's ledger correct.

7 min 1 diagram 1 code practice

3
7.3

Isolation Levels & Read Phenomena

Read Uncommitted → Read Committed → Repeatable Read → Serializable, and the dirty/non-repeatable/phantom reads each level tolerates.

7 min 1 diagram 1 code practice

4
7.4

Indexes

B-Trees, composite and covering indexes, selectivity — how queries actually get fast.

7 min 1 diagram 1 code practice

5
7.5

Joins

JOIN, LEFT JOIN, GROUP BY, and the cost story: joins are the reason you vertically grow a SQL DB.

6 min practice

6
7.6

Normalization

Split data by dependency to kill redundancy and update anomalies: 1NF, 2NF, 3NF.

7 min 1 diagram practice

7
7.7

Denormalization

Deliberately duplicating data for read speed — the moment SQL conversations step into system design.

6 min practice