MLS-C01 Exploratory Data Analysis Practice Question
Exhibit
Refer to the exhibit. Consider the following AWS CLI output from an Amazon Athena query:
QueryExecutionId: "12345678-1234-1234-1234-123456789012"
Query: "SELECT COUNT(*) FROM my_table WHERE col1 IS NULL"
Status: "SUCCEEDED"
ResultConfiguration:
OutputLocation: "s3://my-bucket/athena-results/"
ResultSet:
Rows:
- Data:
- VarCharValue: "_col0"
- Data:
- VarCharValue: "5000"An Athena query SELECT COUNT(*) FROM table WHERE col1 IS NULL returns the value 5000. What does this value represent?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The number of rows where col1 is NULL
The exhibit shows the result of an Athena query that counts the number of rows where col1 is NULL. The value 5000 is that count. Therefore, Option B is correct. Option A is incorrect because the query does not count total rows; it filters for NULLs. Option C is incorrect because the query counts NULL rows, not non-NULL. Option D is incorrect because the query does not use DISTINCT to count distinct values.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The total number of rows in the table
Why it's wrong here
The query only counts rows where col1 is NULL, not the total number of rows.
- ✓
The number of rows where col1 is NULL
Why this is correct
The query counts rows where col1 IS NULL, and the result '5000' is that count.
- ✗
The number of rows where col1 is not NULL
Why it's wrong here
The query counts rows where col1 is NULL, not rows where col1 is not NULL.
- ✗
The number of distinct values in col1
Why it's wrong here
The query counts all NULL rows, not distinct values of col1.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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