SQL Window Function Basics Quiz

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| Questions: 15 | Updated: May 1, 2026
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1. What is the primary purpose of a window function in SQL?

Explanation

A window function in SQL enables users to perform calculations across a specified range of rows, or "window," that are related to the current row. This allows for complex aggregations and analytics without collapsing the result set, preserving individual row details while still providing summary insights.

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About This Quiz
SQL Window Function Basics Quiz - Quiz

This SQL Window Function Basics Quiz evaluates your understanding of window functions\u2014a powerful SQL feature for analyzing data across rows and partitions. Learn how to use aggregate, ranking, and analytic functions over specified windows of data. Perfect for college-level students mastering advanced SQL queries and data analysis techniques.

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2. Which clause defines the subset of rows a window function operates over?

Explanation

The OVER clause specifies the window or set of rows that a window function will analyze. It allows for partitioning and ordering of data within a result set, enabling functions like ROW_NUMBER, RANK, and SUM to perform calculations across defined subsets, rather than the entire dataset.

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3. In a window function, what does PARTITION BY do?

Explanation

PARTITION BY in a window function is used to divide the result set into distinct groups based on specified columns. This allows the window function to perform calculations independently within each group, enabling more granular analysis of data without collapsing it into a single result.

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4. Which of the following is a ranking window function?

Explanation

RANK() is a ranking window function that assigns a unique rank to each row within a partition of a result set, based on the values of specified columns. Unlike aggregate functions like SUM(), AVG(), or COUNT(), which perform calculations over a set of rows, RANK() focuses on ordering individual rows.

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5. What is the difference between RANK() and DENSE_RANK()?

Explanation

RANK() assigns the same rank to tied values but skips subsequent ranks, leading to potential gaps in the ranking sequence. In contrast, DENSE_RANK() also assigns the same rank to ties but maintains a continuous ranking without gaps. This distinction affects how rankings are represented when there are ties in the data.

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6. Which window function returns the value from a specified row within the window?

Explanation

LAG(), LEAD(), and NTH_VALUE() are all window functions that allow access to specific rows within a defined window. LAG() retrieves data from a previous row, LEAD() from a subsequent row, and NTH_VALUE() returns the value from a specified row position. Thus, all three functions can return values from specified rows.

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7. What does LAG() do in a window function?

Explanation

LAG() is a window function that allows users to access data from a previous row within the same result set. It is commonly used to compare values across rows, enabling analysis of trends or changes over time by retrieving the value of a specified column from the preceding row.

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8. In the frame clause, what does ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW mean?

Explanation

ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW specifies a window frame in SQL that includes all rows from the beginning of the partition up to and including the current row. This allows for cumulative calculations, aggregating values from the start of the specified partition to the current point in the dataset.

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9. Which window function assigns a unique sequential number to rows?

Explanation

ROW_NUMBER() is a window function that assigns a unique sequential integer to rows within a partition of a result set, starting at one for the first row. Unlike RANK() or NTILE(), which can assign the same number to ties, ROW_NUMBER() ensures that each row receives a distinct number, making it ideal for unique identification.

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10. What does the NTILE(n) function do?

Explanation

NTILE(n) is a window function in SQL that divides a result set into 'n' equal parts, or buckets. It assigns a bucket number to each row, allowing for easy analysis of data distributions across specified intervals. This is particularly useful for percentile calculations and data segmentation.

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11. Can you use aggregate functions like SUM() and AVG() as window functions?

Explanation

Aggregate functions like SUM() and AVG() can be utilized as window functions by incorporating the OVER clause, allowing calculations across a specified range of rows while retaining individual row details. This capability enhances data analysis by providing insights into subsets of data without collapsing them into single summary values.

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12. What is the correct syntax order for a window function with OVER clause?

Explanation

The syntax for a window function with the OVER clause requires the function to be specified first, followed by the OVER keyword. Inside the parentheses, the PARTITION BY clause can be used to define how to group the data, and the ORDER BY clause specifies the order of the rows within each partition. This structure ensures proper execution of the window function.

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13. Window functions are evaluated ______ the WHERE clause.

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14. The ______ clause in a window function specifies the order of rows within each partition.

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15. FIRST_VALUE() returns the ______ value in the window frame.

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What is the primary purpose of a window function in SQL?
Which clause defines the subset of rows a window function operates...
In a window function, what does PARTITION BY do?
Which of the following is a ranking window function?
What is the difference between RANK() and DENSE_RANK()?
Which window function returns the value from a specified row within...
What does LAG() do in a window function?
In the frame clause, what does ROWS BETWEEN UNBOUNDED PRECEDING AND...
Which window function assigns a unique sequential number to rows?
What does the NTILE(n) function do?
Can you use aggregate functions like SUM() and AVG() as window...
What is the correct syntax order for a window function with OVER...
Window functions are evaluated ______ the WHERE clause.
The ______ clause in a window function specifies the order of rows...
FIRST_VALUE() returns the ______ value in the window frame.
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