Checkpoint: Preserve Accounts and Bound Graph Walks

Reason about missing accounts, signed balances, duplicate paths, and termination. Select one option per multiple-choice question; use integer-only short answers.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. Account 8 has only pending entries and account 9 has no entries. A LEFT JOIN is followed by WHERE e.status = 'posted'. Which repair preserves both accounts?

Select one answer.

Add COALESCE around the current SUM without moving the filter. Add OR e.account_id IS NULL to WHERE; this always preserves both. Move eligibility into ON, or use conditional aggregation without the filtering WHERE. Use an INNER JOIN and then DISTINCT account IDs.

2. Before/on the date cutoff, one account has posted +800, posted +800, posted -350, and pending +900; it also has posted +200 after cutoff. What is balance_cents? Enter one integer.

3. Seed A has edges A->B, A->C, B->C, C->A, C->D, D->E. What is the two-hop result after taking minimum depths?

Select one answer.

A:0, B:1, C:1, D:2 A:2, B:1, C:2, D:2 A:0, B:1, C:1, D:2, E:3 B:1, C:1, D:2

4. An unbounded recursive CTE emits (account_id, depth) on a cyclic graph. Why is replacing UNION ALL with UNION insufficient to guarantee termination?

Select one answer.

UNION always keeps duplicate rows. UNION follows incoming instead of outgoing edges. The final ORDER BY disables duplicate removal. A revisited account with a larger depth is a different row.

5. Flagged seeds are P and S. Edges are P->Q, Q->R, R->S, S->R, and R->T. What is the minimum hop depth of T under the two-hop rule? Enter one integer.

6. The ledger exercise uses DATE entry_ts and reports as-of through April 30. A new system stores UTC TIMESTAMPTZ. Which predicate includes all history through April 30 UTC and excludes May 1?

Select one answer.

entry_ts <= TIMESTAMPTZ '2025-04-30 00:00:00+00' entry_ts < TIMESTAMPTZ '2025-05-01 00:00:00+00' entry_ts = DATE '2025-04-30' entry_ts <= TIMESTAMPTZ '2025-05-01 00:00:00+00'

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