Difference between scalar, table-valued, and aggregate functions in SQL server?

Question

What is the difference between scalar-valued, table-valued, and aggregate functions in SQL server? And does calling them from a query need a different method, or do we call

Answer 1

Aggregate and Scalar functions both return a single value but Scalar functions operate based on a single input value argument while Aggregate functions operate on a single input set of values (a collection or column name). Examples of Scalar functions are string functions, ISNULL, ISNUMERIC, for Aggregate functions examples are AVG, MAX and others you can find in Aggregate Functions section of Microsoft website.

Table-Valued functions return a table regardless existence of any input argument. Execution of this functions is done by using them as a regular physical table e.g: SELECT * FROM fnGetMulEmployee()

This following link is very useful to understand the difference: https://www.dotnettricks.com/learn/sqlserver/different-types-of-sql-server-functions