A function is a syntactic structure that returns a value derived from applying the function to its arguments. The XDB Server provides standard SQL functions, including SUM, MIN, MAX, COUNT, and AVG, as well as XDB Server-specific extensions, which usually begin with an "X".
Functions are frequently used in the SELECT clause and WHERE clause of SELECT commands, as well as in the WHERE clause of UPDATE and DELETE commands. Functions may also appear in HAVING clauses. Their use is not limited to these cases, however. For example, functions that involve arguments that can be evaluated as constants can be used in the VALUES clause of INSERT commands.
For maximum flexibility, many of the functions can be nested within one another. In addition, functions can make use of the special keywords (for example, CURRENT DATE, CURRENT TIME).