Data Scholar

Course

SQL Basics

Zero to genuinely solid SQL: every query pattern you must own before any data interview, drilled with runnable, interview-style questions.

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The foundation everything else builds on. Start from your very first SELECT and finish able to write correct, confident SQL under interview pressure.

What makes it different: every concept is drilled with runnable questions in a real in-browser database, the difficulty ramps from beginner to the tricky questions top companies actually ask, and it is strict standard SQL throughout (no vendor dialect tricks).

You will master: SELECT and filtering, sorting and limiting, all the joins (and what they really do), aggregation and GROUP BY discipline, HAVING vs WHERE, subqueries and CTEs, set operations, NULL logic (the silent killer in interviews), CASE reasoning, and a first taste of window functions.

Finish this, then pick the specialization that matches your target role: SQL for Data Analytics, SQL for Data Engineers, or SQL for AI Engineers.

Curriculum

M1SELECT fundamentals
  1. 1.1Projection: SELECT, expressions, aliases
  2. 1.2Filtering: WHERE and boolean logic
  3. 1.3Shaping: ORDER BY, LIMIT, DISTINCT
  4. 1.4Exercises: SELECT fundamentals
M2NULL, the silent killer
  1. 2.1Three-valued logic
  2. 2.2NULLs in aggregates, COALESCE, and sorting
  3. 2.3Exercises: NULL logic
M3Aggregation and GROUP BY discipline
  1. 3.1The aggregate functions
  2. 3.2GROUP BY and HAVING
  3. 3.3Conditional aggregation
  4. 3.4Exercises: aggregation
M4Joins, really
  1. 4.1INNER JOIN mechanics
  2. 4.2LEFT JOIN and the ON vs WHERE trap
  3. 4.3Self joins, FULL OUTER, CROSS, and EXISTS
  4. 4.4Exercises: joins
M5Subqueries and CTEs
  1. 5.1Subqueries: scalar, IN, EXISTS, correlated
  2. 5.2CTEs: queries that read like reasoning
  3. 5.3Exercises: subqueries and CTEs
M6Set operations
  1. 6.1UNION, INTERSECT, EXCEPT
  2. 6.2Exercises: set operations
M7CASE and the expression toolkit
  1. 7.1CASE logic
  2. 7.2Strings, dates, and numbers
  3. 7.3Exercises: CASE and expressions
M8First window functions
  1. 8.1Ranking: ROW_NUMBER, RANK, DENSE_RANK
  2. 8.2Windowed aggregates, LAG, and running totals
  3. 8.3Exercises: window functions
M9The gauntlet
  1. 9.1How to attack an unseen question
  2. 9.2Exercises: the gauntlet