Master SQL through topic-driven practice

Select columns, filter rows, remove duplicates, and order query results.

Practice SQL WHERE clauses with realistic boundary, NULL, text, date, exclusion, and production-filtering problems.

Practice deterministic top-N, cutoff ties, offset pagination, composite keyset cursors, and resumable bounded batches.

Practice production-oriented string cleanup, numeric transformations, NULL handling, tolerant conversion, and delimiter parsing.

Practice deterministic SQL ordering with tie-breakers, custom priorities, NULL placement, expressions, joined data, aggregates, and portable top-N patterns.

Practice reliable INNER, LEFT, FULL, CROSS, self, semi, anti, range, temporal, and many-to-many join patterns.

Practice scalar, derived-table, correlated, EXISTS, NULL-safe anti-subquery, quantified, and row-subquery patterns.

Practice modular CTE pipelines, deterministic window analytics, period comparisons, deduplication, frames, and gaps-and-islands.

Build reliable SQL metrics from aggregate functions through grain, fan-out, weighted ratios, rollups, percentiles, and approximate counts.

Solve deterministic ranking, top-N, distribution, positional-frame, and rolling-window problems.

Detect identity collisions, profile NULL-aware conflicts, and compare deterministic survivors with production-safe SQL.

Build NULL-aware classifications, precedence-safe decisions, flags, scores, and guarded calculations with portable CASE expressions.

Practice safe SQL data changes, schema evolution, retry-safe upserts, transactions, rollback, views, and indexes in isolated databases.

Practice date arithmetic, safe timestamp ranges, calendar bucketing, dense time series, rolling windows, growth, and cohort analysis.

Query organization charts, trees, and parent-child relationships.