DBMS: Function (Definitions)

"A set of instructions that operates as a single logical unit, can be called by name, accepts input parameters, and returns information. In programming languages such as C, a function is a named subroutine of a program that encapsulates some logic. The function can be called by name, using parameters to pass data into the function and retrieve data produced by the function. In Transact-SQL, a function is a unit of syntax consisting of a keyword and, usually, a set of parameters. There are several categories of Transact-SQL functions: string, math, system, niladic, text and image, date, aggregate, and conversion functions." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A program that returns a value to the program or environment from which it is called." (Bill Pribyl & Steven Feuerstein, "Learning Oracle PL/SQL", 2001)

"A section of code that operates as a single logical unit. Transact-SQL supports both built-in functions and user-defined functions. The built-in functions cannot be modified by SQL Server 2000 users, whereas users can create and modify user- defined functions." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A named set of predefined programming language commands that performs a specific task given zero, one, or more arguments and returns a value." (Bob Bryla, "Oracle Database Foundations", 2004)

"A programming unit or expression returning a single value, also allowing determinant values to be passed in as parameters. Thus, parameter values can change the outcome or return result of a function. The beauty of a function is that it is self-contained and can thus be embedded into an expression." (Gavin Powell, "Beginning Database Design", 2006)

"A set of instructions that operates as a single logical unit." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"A centralized, server-based routine that can be included as part of your Transact-SQL statements. Typically used to streamline logic and reduce the amount of required programming effort, you can build your own functions." (Robert D Schneider & Darril Gibson, "Microsoft SQL Server 2008 All-in-One Desk Reference For Dummies", 2008)

"Functions are routines that can accept parameters, perform an action, and return the result of that action. SQL Server includes many built-in functions. User- defined functions can be created to meet specific needs." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"A piece of code that operates as a single logical unit. A function is called by name, accepts optional input parameters, and returns a status and optional output parameters. Many programming languages support functions, including C, Visual Basic, and Transact-SQL. Transact-SQL supplies built-in functions, which cannot be modified, and supports user-defined functions, which can be created and modified by users." (Jim Joseph, "Microsoft SQL Server 2008 Reporting Services Unleashed", 2009)

"A small program that performs one task and returns a single value. It may be built into the SQL language or written by a user, database administrator, or application programmer." (Jan L Harrington, "SQL Clearly Explained" 3rd Ed., 2010)

"A piece of code that operates as a single logical unit. A function is called by name, accepts optional input parameters, and returns a status and optional output parameters. Many programming languages support functions." (SQL Server 2012 Glossary, "Microsoft", 2012)

"A predefined algorithm supported by the DBMS for converting, manipulating, or calculating data based upon input. Functions can be used within SQL statements any place an expression can be used." (Craig S Mullins, "Database Administration", 2012)

"A relationship between a set of input data values and a set of result values that is used to extend and customize SQL or XQuery. Functions are invoked from elements of SQL statements such as the select list or the FROM clause and from XQuery as primary expressions." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)