In SQL, what does the function COUNT() do?

The function COUNT() in SQL is designed to count the number of rows in a specified dataset, typically within a table. It returns the total number of rows that match a specified condition or that are present in the entire table if no condition is provided. This is especially useful for aggregating data and understanding how many records meet certain criteria in database operations.

When using COUNT(), it can be applied in various scenarios, such as counting all entries in a table or counting specific entries that fulfill certain conditions through the use of a WHERE clause. This function is often utilized in conjunction with GROUP BY to return counts of rows for each group.

The other choices relate to different functionalities: calculating totals (which would involve something like SUM()), finding maximum values (which pertains to the MAX() function), or defining variables (not directly related to SQL aggregate functions). Therefore, the primary role of COUNT() is to provide a straightforward count of rows, making it an essential function for database querying and analysis.