Question

Which SQL aggregate function returns the total number of unique values in a column?

• A. COUNT (DISTINCT column)
• B. TOTAL (DISTINCT column)
• C. UNIQUE (column)
• D. DISTINCT (column)

Answer 1

Answer:

A. COUNT (DISTINCT column)

• The COUNT DISTINCT function returns the number of unique values in the column or expression, as the following example shows.
• SELECT COUNT(DISTINCT column_name) FROM table_name; This simple query provides you with the frequency of unique values in the respective column of the passed table.
• It's a very useful feature in SQL for tasks like finding the number of different categories, unique customers, or distinct items in your dataset.