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Explanation:

The query:

SELECT COUNT(DISTINCT *) FROM user

SELECT COUNT(DISTINCT *) FROM user

is asking how many distinct rows exist in the table.

Key concept (important for Databricks / Spark SQL):

DISTINCT * means Spark compares entire rows, not individual columns.
COUNT(DISTINCT ...) counts how many unique rows exist.
Unlike COUNT(column), this does not exclude rows just because they contain NULL.

Row-by-row analysis:

Row	userId	username	email	Distinct?
1	1	john.smith	john.smith@com	✅
2	2	NULL	david.clear@com	✅
3	3	kevin.smith	kevin.smith@com	✅

All three rows are different, even though one row contains NULL.

✅ Correct Answer: A (3)

Why the others are wrong:

B (2): Incorrect—no duplicate rows exist.
C (1): Would require all rows to be identical.
D (NULL): COUNT never returns NULL.

Explanation:

The query:

SELECT COUNT(DISTINCT *) FROM user

SELECT COUNT(DISTINCT *) FROM user

is asking how many distinct rows exist in the table.

Key concept (important for Databricks / Spark SQL):

DISTINCT * means Spark compares entire rows, not individual columns.
COUNT(DISTINCT ...) counts how many unique rows exist.
Unlike COUNT(column), this does not exclude rows just because they contain NULL.

Row-by-row analysis:

Row	userId	username	email	Distinct?
1	1	john.smith	john.smith@com	✅
2	2	NULL	david.clear@com	✅
3	3	kevin.smith	kevin.smith@com	✅

All three rows are different, even though one row contains NULL.

✅ Correct Answer: A (3)

Why the others are wrong:

B (2): Incorrect—no duplicate rows exist.
C (1): Would require all rows to be identical.
D (NULL): COUNT never returns NULL.

Comments (1)

Ronnie SwansonJan 19, 2026 8:34 PM

what on earth is this question

LeetQuiz .Jan 23, 2026 10:34 AM

Thanks for pointing this out! You’re right—the table was missing in the original post. I’ve now added it so the question has full context. We appreciate the feedback!

What would be the expected result of executing the query `SELECT COUNT(DISTINCT *) FROM user` on a table below:

userId username email
1 john.smith john.smith@com
2 NULL david.clear@com
3 kevin.smith kevin.smith@com

userId	username	email
1	john.smith	john.smith@com
2	NULL	david.clear@com
3	kevin.smith	kevin.smith@com

Real Exam

Last updated: January 23, 2026 at 10:32

89.4%

2.5%

2.2%

NULL

5.9%

Databricks Certified Data Engineer - Associate

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Key concept (important for Databricks / Spark SQL):

Row-by-row analysis:

Why the others are wrong:

Key concept (important for Databricks / Spark SQL):

Row-by-row analysis:

Why the others are wrong:

Comments (1)

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Comments (1)

What would be the expected result of executing the query SELECT COUNT(DISTINCT *) FROM user on a table below: userIdusernameemail1john.smithjohn.smith@com2NULLdavid.clear@com3kevin.smithkevin.smith@com

What would be the expected result of executing the query `SELECT COUNT(DISTINCT *) FROM user` on a table below:

userId username email
1 john.smith john.smith@com
2 NULL david.clear@com
3 kevin.smith kevin.smith@com