REPOSITORY CODING · HARD
COUNT(column) skips nulls, COUNT(*) counts every row, and SUM over empty or all-null groups is null
COUNT(column) skips nulls, COUNT(*) counts every row, and SUM over empty or all-null groups is null. The complete application includes native models, services, repository projections, a working preview and visible acceptance cases. Preserve the other documented invariants and run bash test/run.sh.
relational-algebraRelational bag algebra workbench
Work through a real codebase.
Choose an environment, investigate the existing implementation and use the tests to check your change. Sign in to open a workspace; execution and Ono usage follow your plan’s allowances.
Task requirements and environments
JavaScript · 80 minute session
- SQL join equality never matches null to null. Left joins retain unmatched rows with the complete right-side null schema.
- Filtering preserves SQL three-valued negation, and projection preserves duplicate rows unless DISTINCT is explicitly requested.
- COUNT(column) skips nulls, COUNT(*) counts every row, and SUM over empty or all-null groups is null.
- Synthetic tables are scoped by tenant. Plans support scan, inner/left join, three-valued filters, bag projection, distinct and grouped aggregates. Each accepted command advances revision and appends audit; failed journals roll back tables and audit. Native PostgreSQL/MongoDB variants persist these same aggregates.
MEAN · 80 minute session
- SQL join equality never matches null to null. Left joins retain unmatched rows with the complete right-side null schema.
- Filtering preserves SQL three-valued negation, and projection preserves duplicate rows unless DISTINCT is explicitly requested.
- COUNT(column) skips nulls, COUNT(*) counts every row, and SUM over empty or all-null groups is null.
- Synthetic tables are scoped by tenant. Plans support scan, inner/left join, three-valued filters, bag projection, distinct and grouped aggregates. Each accepted command advances revision and appends audit; failed journals roll back tables and audit. Native PostgreSQL/MongoDB variants persist these same aggregates.
MERN · 80 minute session
- SQL join equality never matches null to null. Left joins retain unmatched rows with the complete right-side null schema.
- Filtering preserves SQL three-valued negation, and projection preserves duplicate rows unless DISTINCT is explicitly requested.
- COUNT(column) skips nulls, COUNT(*) counts every row, and SUM over empty or all-null groups is null.
- Synthetic tables are scoped by tenant. Plans support scan, inner/left join, three-valued filters, bag projection, distinct and grouped aggregates. Each accepted command advances revision and appends audit; failed journals roll back tables and audit. Native PostgreSQL/MongoDB variants persist these same aggregates.