Functions are similar to operators in that they manipulate data items and return a result. Functions differ from operators in the format of their arguments. This format enables them to operate on zero, one, two, or more arguments:
function(argument, argument, ...)
A function without any arguments is similar to a pseudocolumn (refer to Chapter 3, "Pseudocolumns"). However, a pseudocolumn typically returns a different value for each row in the result set, whereas a function without any arguments typically returns the same value for each row.
This chapter contains these sections: