AI-assisted — how our quizzes are made
SELECT basics, WHERE clause, comparison and logical operators, NULL handling, ORDER BY, LIMIT/OFFSET, DISTINCT, aliases, and CASE expressions
30 questionsINNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, CROSS JOIN, self-joins, join conditions, and multi-table queries
35 questionsNormalization forms, denormalization, foreign keys, constraints, primary keys, surrogate keys, entity relationships
ROW_NUMBER, RANK, DENSE_RANK, PARTITION BY, LEAD, LAG, FIRST_VALUE, LAST_VALUE, window frames
35 questionsGROUP BY, COUNT, SUM, AVG, MIN, MAX, HAVING, and combining aggregation with filtering.
30 questionsCorrelated and non-correlated subqueries, CTEs (WITH clause), recursive CTEs, EXISTS/NOT EXISTS, and query readability.
30 questionsINSERT, UPDATE, DELETE, UPSERT (INSERT ... ON CONFLICT / MERGE), transactions, and bulk operations.
30 questionsB-tree and hash indexes, composite indexes, covering indexes, query plans (EXPLAIN), index selectivity, and when not to index.
30 questionsWhat does PARTITION BY do in a window function?
Divides results into groups for separate calculations
Filters rows
Orders results
Creates temporary tables
What does COUNT(*) count?
Only non-NULL values in all columns
All rows including those with NULLs
Distinct values only
Only rows matching the WHERE clause after grouping