Week 21: Quiz (10 questions, 8/10 to pass)

Answer each, then check against the answer key. Each question ends with a pointer to the Concepts section (§) or notebook cell it tests.

1. (MCQ) In Unity Catalog's three-level namespace catalog.schema.object, which of the following is a valid object type? (see Concepts §UC is governance)

   • A) metastore
   • B) volume
   • C) workspace
   • D) compute plane

2. (MCQ) You run VACUUM on a Delta table with default settings, then try SELECT * FROM tbl TIMESTAMP AS OF '30 days ago'. What happens? (see Concepts §Delta gives time travel)

   • A) It always works, VACUUM only compacts files
   • B) It fails, because data files older than 7 days were permanently deleted
   • C) It returns an empty table but no error
   • D) It returns an error only if the table is partitioned

3. (Short answer) Why is a Unity Catalog privilege model described as "additive-only," and what are the two privilege kinds a principal needs to read zrl_.silver.shipments? (see Concepts §privilege model)

4. (MCQ) In notebook 02-medallion-sql.ipynb, the silver query dedupes with ROW_NUMBER() OVER (PARTITION BY shipment_id ORDER BY planned_departure) and keeps WHERE rn = 1. What would break if you partitioned by carrier_id instead? (see Concepts §medallion; notebook 02 cell 4)

   • A) Nothing, carrier_id is also unique per row
   • B) Distinct shipments from the same carrier would be collapsed
   • C) The imputation would stop working
   • D) Time travel would fail

5. (MCQ) Which statement about managed vs. external tables is correct? (see Concepts §Unity Catalog)

   • A) DROP TABLE deletes data for both
   • B) DROP TABLE deletes data only for managed tables
   • C) External tables cannot be Delta
   • D) Managed tables require a LOCATION clause

6. (Short answer) Notebook 01-unity-catalog-and-delta-lab.ipynb ends by printing bronze rows and time-travel versions. Explain why the time_travel_demo table has exactly 2 versions after the lab runs. (see Notebook walkthrough; notebook 01 cells 9 to 12)

7. (MCQ) You want a filter column (carrier_id) to enable data skipping but you anticipate re-keying the layout later. Which feature should you use on a new table? (see Concepts §Delta gives time travel)

   • A) Hive partitioning
   • B) ZORDER BY only
   • C) Liquid clustering (CLUSTER BY)
   • D) OPTIMIZE only

8. (Short answer) In the worked GRANT example, why must zrl_analysts receive USE CATALOG ON CATALOG zrl_ and USE SCHEMA and SELECT rather than just SELECT on the table? (see Concepts §privilege model)

9. (MCQ) The notebook %sql cell CREATE OR REPLACE TABLE shipments_bronze AS SELECT * FROM read_files('/Volumes/zrl_/zorologistics/raw/shipments.csv', format => 'csv', header => true, inferSchema => true) produces a Delta table because… (see Notebook walkthrough)

   • A) read_files only outputs Delta
   • B) Delta is the default table format on Databricks unless you say otherwise
   • C) the CSV was already converted by the generator
   • D) it is a streaming table

10. (MCQ) Which of the following is a consequence of liquid clustering rather than Hive partitioning? (see Concepts §Delta gives time travel)

• A) You can change clustering keys without rewriting the table
• B) It makes time travel impossible
• C) It requires enabling deletion vectors
• D) It is incompatible with VACUUM

Answer key

1. B: volume. A volume is a governed object at the catalog.schema.object level; the metastore is the registry above the catalog, and workspace/compute plane are platform concepts, not UC objects.

2. B: it fails. VACUUM permanently removes data files older than the retention window (default 7 days), so time travel past that window is impossible.

3. Additive-only means there is no DENY: a principal can only gain privileges, and the default is "nothing." To read the table a principal needs traversal (USE CATALOG zrl_ + USE SCHEMA silver) and action (SELECT on the table). Both kinds are required.

4. B. Partitioning by carrier_id and keeping one row per partition would collapse all of a carrier's distinct shipments into one; shipment_id is the natural key that must stay unique.

5. B. DROP TABLE deletes data only for managed tables; external tables drop metadata only (the data stays in your storage).

6. Two versions = the CREATE OR REPLACE (version 1, 1,000 rows) and the INSERT (version 2, another 1,000 rows). Each write appends a new transaction log entry, so DESCRIBE HISTORY shows exactly two versions, and VERSION AS OF 1 reads the 1,000-row state while current reads 2,000.

7. C: liquid clustering. CLUSTER BY colocates data for skipping and lets you change keys without a rewrite; ZORDER BY alone cannot be re-keyed without rewriting.

8. Privileges inherit down, but traversal and action are separate. SELECT on a table is not enough by itself, the principal must first reach the container with USE CATALOG and USE SCHEMA. UC requires the traversal chain plus the action; a bare SELECT grant without USE grants on the parents would not permit the read.

9. B. Delta is the default storage layer, every table created on Databricks is a Delta table unless configured otherwise, so CREATE … AS SELECT FROM read_files lands as a governed Delta table.

10. A. Liquid clustering's headline benefit over Hive partitioning/Z-order is that you can change the clustering keys without rewriting the table.