CERTIFIED-MACHINE-LEARNING-PROFESSIONAL Question #57: Real Exam Question with Answer & Explanation

Question

After a data scientist noticed that a column was missing from a production feature set stored as a Delta table, the machine learning engineering team has been tasked with determining when the column was dropped from the feature set. Which of the following SQL commands can be used to accomplish this task?

Options

• AVERSION
• BDESCRIBE
• CHISTORY
• DDESCRIBE HISTORY
• ETIMESTAMP

Explanation

DESCRIBE HISTORY <table_name> is the correct Delta Lake command because it returns a full audit log of every operation performed on the table - including schema changes like dropping a column - along with timestamps and operation metadata, making it straightforward to pinpoint exactly when the column was removed.

Why the distractors are wrong:

• A. VERSION - Not a standalone command; it's a clause used in Delta time travel queries (e.g., SELECT * FROM table VERSION AS OF 3) to read a past snapshot, not to inspect change history.
• B. DESCRIBE - Returns the current schema of a table (columns, types, nullability). It has no awareness of past states.
• C. HISTORY - Not a valid standalone SQL command in Delta Lake; you need the full DESCRIBE HISTORY syntax.
• E. TIMESTAMP - Also a time travel clause, not a command. Used as SELECT * FROM table TIMESTAMP AS OF '2024-01-01' to query a past state, not to audit changes.

Memory tip: Think of it as "describe what happened in the history" - you're describing the table's changelog, not its current structure. If you ever confuse B and D, remember: plain DESCRIBE tells you what a table looks like now, while DESCRIBE HISTORY tells you what happened to it over time.

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