Scalar functions take input parameters and return a single value result. Some examples of standard SQL scalar functions are CHARACTER_LENGTH, POSITION, and SUBSTRING.
Aggregate functions produce summary results. They differ from scalar functions in that they take grouped sets of relational data, make a pass over each group, and return one result for the group. Some examples of standard SQL aggregate functions are AVG, SUM, MAX, and MIN.
The built-in functions, or special register functions, which have no arguments, return various information about the system and can be used like other literals within SQL expressions. In an SQL query, the appropriate system value is substituted by the Parser after optimization but prior to executing a query using a cachable plan.
Available built-in functions include all of the following:
For the names, parameters, return values, and other details of scalar and aggregate functions, see SQL Functions, Operators, Expressions, and Predicates.
For information on clauses and phrases, see SQL Functions, Operators, Expressions, and Predicates.