A function is a MySQL command used in an SQL statement that takes one or more arguments and returns a value based on the values supplied. Just as with expressions, you can use a function anywhere a fixed value could otherwise be used, or to manipulate the value returned in a database column.
Function names are not case sensitive in MySQL. For example, you can use ROUND(), Round(), or round()—these all perform the same function call.
To pass a function more than one argument, separate the values in parentheses ...