DB Playground — Week 2

last run ›

Click New DB to seed the schema and start the assignment.

▾Part 1 — Aggregates 0/8

1.1

Count the total number of tasks

⊞ expected output

1.2

Tasks per user (include 0-task users)

💡 hint

LEFT JOIN keeps users even when they have no matching tasks.

⊞ expected output

1.3

Number of tasks per status

⊞ expected output

1.4

User with the most tasks

💡 hint

GROUP BY user, then ORDER BY count DESC LIMIT 1.

⊞ expected output

1.5

Avg tasks per user (≥1 task only)

💡 hint

Use a subquery to count per user first, then AVG on the outer query.

⊞ expected output

1.6

Earliest and latest due dates

⊞ expected output

1.7

Categories ordered by task count

⊞ expected output

1.8

Users with more than 2 tasks

💡 hint

HAVING filters after aggregation — like WHERE but for GROUP BY results.

⊞ expected output

▾Part 3 — Transactions 0/2

3.1

Reassign tasks + delete user (commit)

⊞ expected output

3.2

Deliberate rollback demo

💡 hint

Try inserting a task with status_id = 9999 to force a constraint violation.

⊞ expected output

▾Part 4 — Combined 0/2

4.1

Transaction: create "Urgent" + assign tasks

💡 hint

INSERT OR ROLLBACK will auto-rollback on a duplicate category name.

4.2

Dashboard summary in a single SELECT

💡 hint

SUM(CASE WHEN ... THEN 1 ELSE 0 END) counts matching rows conditionally.

⊞ expected output

▾Quick Refs

List all tables

Inspect task schema

Browse tasks

Browse users

Browse statuses