Which function returns the number of unique columns in an array?

Which function returns the number of unique columns in an array?

• A. count distinct
• B. count
• C. avg
• D. max

Answer: (A)

Counting how many different values appear in an array is what this question is getting at. To get that number, you need a function that counts only unique items, effectively ignoring duplicates. That’s what a count distinct operation does: it looks at the values, keeps one copy of each distinct value, and returns how many there are. The other options perform different tasks: a simple count tallies every element, including duplicates; avg computes the average of all elements; max returns the largest element. For example, with [5, 5, 7, 3, 7], there are three distinct values (3, 5, 7), so count distinct yields 3, while count would yield 5, avg would be 5.4, and max would be 7. Hence, count distinct is the correct choice.

Counting how many different values appear in an array is what this question is getting at. To get that number, you need a function that counts only unique items, effectively ignoring duplicates. That’s what a count distinct operation does: it looks at the values, keeps one copy of each distinct value, and returns how many there are. The other options perform different tasks: a simple count tallies every element, including duplicates; avg computes the average of all elements; max returns the largest element. For example, with [5, 5, 7, 3, 7], there are three distinct values (3, 5, 7), so count distinct yields 3, while count would yield 5, avg would be 5.4, and max would be 7. Hence, count distinct is the correct choice.