Structured Query Language (SQL) - Cultural View of Technology

XLeratorDB 122
XLeratorDB requires Microsoft SQL Server 2005 or SQL Server 2005 Express editions, or later (compatibility
mode 90 or higher). [9] The product installs with PERMISSION_SET=SAFE. SAFE mode, the most restrictive
permission set, is accessible by all users. Code executed by an assembly with SAFE permissions cannot access
external system resources such as files, the network, the internet, environment variables, or the registry. [10]
Functions
In computer science, a function is a portion of code within a larger program which performs a specific task and is
relatively independent of the remaining code. As used in database and spreadsheet applications these functions
generally represent mathematical formulas widely used across a variety of fields. While this code may be
user-generated, it is also embedded as a pre-written sub-routine in applications. These functions are typically
identified by common nomenclature which corresponds to their underlying operations: e.g. IRR identifies the
function which calculates Internal Rate of Return on a series of periodic cash flows.
Function uses
As sub-routines functions can be integrated and used in a variety of ways, and in a wide variety of larger, more
complicated applications. Within large enterprise applications they may, for example, play an important role in
defining business rules or risk management parameters, while remaining virtually undetected by end users. Within
database management systems and spreadsheets, however, these kinds of functions also represent discrete sets of
tools; they can be accessed directly and utilized on a stand-alone basis, or in more complex, user-defined
configurations. In this context, functions can be used for business intelligence and ad hoc analysis of data in fields
such as finance, statistics, engineering, math, etc.
Function types
XLeratorDB uses three kinds of functions to perform analytic operations: scalar, aggregate, and a hybrid form
which WestClinTech calls Range Queries. Scalar functions take a single value, perform an operation and return a
single value. [11] An example of this type of function is LOG, which returns the logarithm of a number to a specified
base. [12] Aggregate functions operate on a series of values but return a single, summarizing value. An example of
this type of function is AVG, which returns the average of values in a specified group. [13]
In XLeratorDB there are some functions which have characteristics of aggregate functions (operating on multiple
series of values) but cannot be processed in SQL CLR using single column inputs, such as AVG does. For example,
irregular internal rate of return (XIRR), a financial function, operates on a collection of cash flow values from one
column, but must also apply variable period lengths from another column and an initial iterative assumption from a
third, in order to return a single, summarizing value. WestClinTech documentation notes that Range Queries specify
the data to be included in the result set of the function independently of the WHERE clause associated with the
T-SQL statement, by incorporating a SELECT statement into the function as a string argument; the function then
traps that SELECT statement, executes it internally and processes the result. [14]
Some XLeratorDB functions that employ Range Queries are: NPV, XNPV, IRR, XIRR, MIRR,
MULTINOMIAL, and SERIESSUM. Within the application these functions are identified by a "_q" naming
convention: e.g. NPV_q, IRR_q, etc. [15]