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SQL practice

NULLs in aggregates

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Column x holds 10, NULL and 20. What does SQLite return?

SELECT AVG(x) FROM t;

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No signup · first signal after 5 answers · your score at session end

Predict query results — and learn why

Master SQL by predicting what queries return — SELECT and WHERE filtering, JOINs, GROUP BY with aggregates (COUNT/SUM/AVG/MIN/MAX), HAVING, ORDER BY and LIMIT, DISTINCT, and the NULL semantics that trip people up (= NULL vs IS NULL, COUNT(col) vs COUNT(*)). Every answer is computed by running real SQLite, so the explanations are exact. Output-prediction practice that builds genuine query fluency for interviews. Part of the Developer track.

• Meets you at your level — never too easy, never too hard.

• Adapts every question to how you’re doing.

• Tracks your level over time. Skill practice, not a test.

New here? Read the SQL guide

A free 17-minute primer — the mental model, the mistakes beginners make, and what to practice first.

Curriculum

323 concepts across 32 chapters, from foundations through advanced practice — each one a concept the adaptive question bank can teach and test.

A. The relational model and what a query is

B. NULL and the three-valued logic that follows

C. Filtering with WHERE

D. Sorting, paging and DISTINCT

E. Aggregation and grouping

F. Joins

G. Subqueries and CTEs

H. Window functions

I. Set operations

J. Data types

K. Expressions and functions

L. Modifying data

M. Constraints and integrity

N. Indexes

O. Transactions and concurrency

P. Query planning and performance

Q. Security

R. Schema design and normalization

S. JSON and semi-structured data

T. Views, functions and procedural extensions

U. Dialect differences and portability

V. Full-text search

W. Arrays

X. Dates, times and time zones

Y. Sequences, identity and generated keys

Z. Partitioning and inheritance

AA. Locking, blocking and retry

AB. MVCC, physical storage and vacuum

AC. Server-side routines and error handling

AD. Sessions, connections and server settings

AE. Backup, restore and replication

AF. Extensions and foreign data

View the full curriculum →

Keentune is not affiliated with or endorsed by the organizations whose documentation informs these maps.

Start practicing — it’s free

No signup · first signal after 5 answers · your score at session end

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SQL on exams

SQL is one of the skills tested on this exam. Each prep page lays out what the real test covers and where this skill fits.

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