Junior
Relational modeling: tables, keys and relationships
How to represent the world in tables: primary key, foreign key and the 1:1, 1:N and N:N relationships that structure every database.
Jun 24, 2026
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Data
What a data professional needs to master at each stage of their career. From relational modeling to real-time data streaming — the concepts that show up in technical interviews and in everyday work, explained directly. Filter by level below.
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Junior
SQL beyond the basics: aggregations, GROUP BY and subqueries
Moving past the simple SELECT: COUNT/SUM/AVG, GROUP BY with HAVING, subqueries and CTEs to answer real questions with data.
Jun 22, 2026
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Junior
Normalization: 1NF, 2NF and 3NF without memorizing
Why duplicated data becomes a bug. The three normal forms explained with a single example, and when to denormalize on purpose.
Jun 20, 2026
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Mid-level
Indexes and performance: why your query is slow
How an index works (the book index analogy), B-tree, when it helps, when it hurts and how to read an execution plan.
Jun 17, 2026
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Mid-level
Dimensional modeling: fact, dimension and the data warehouse
Why the transactional system's model doesn't work for analysis. Fact and dimension tables, star schema and data warehouse basics.
Jun 15, 2026
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Mid-level
ETL and data pipelines: from raw to analytics
Extract, transform and load — or ELT? How data travels from source to report, and why orchestration and idempotency matter.
Jun 13, 2026
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Senior
NoSQL: document, key-value, column and graph — when to use each
The four types of NoSQL database, what each one solves, and why 'NoSQL is faster' is the wrong answer in an interview.
Jun 10, 2026
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Senior
Partitioning and sharding: scaling the database
When one machine isn't enough: vertical and horizontal partitioning, sharding, the partition key and the cost of cross-shard queries.
Jun 8, 2026
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Senior
Streaming data: batch vs real time (Kafka & co.)
Processing data as it arrives, not hour by hour. Batch vs streaming, the event log, and what exactly-once really means.
Jun 6, 2026
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Self-assessment: where are you?
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Quiz: test what you learned
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