User-defined function: Difference between revisions

Revision as of 17:20, 11 November 2015

Revision as of 23:04, 10 December 2015

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A '''user-defined function''' ('''UDF''') is a [[function (programming)|function]] provided by the user of a program or environment, in a context where the usual assumption is that functions are built into the program or environment.

==BASIC language==

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==Databases==

In SQL databases, a UDFuser-defined function provides a mechanism for extending the functionality of the [[database server]] by adding a function that can be evaluated in SQL statements. The [[SQL:2003|SQL]] standard distinguishes between [[Scalar (computing)|scalar]] and table functions. A scalar function returns only a single value (or [[null (SQL)|NULL]]), whereas a table function returns a (relational) table comprising zero or more rows, each row with one or more columns.

User-defined functions in SQL are declared using the <code>CREATE FUNCTION</code> statement. For example, a function that converts Celsius to Fahrenheit might be declared like this:

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*Scalar functions.

*Inline table-valued functions.

*Multistatement tableMultistatementtable-valued functions.

Scalar functions return a single data value (not a table) with RETURNS clause. Scalar functions can use all scalar data types, with exception of timestamp and user-defined data types.

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|title=LanguageManual UDF - Apache Hive - Apache Software Foundation

|work=

|publisher=

|publishe=

|date=26 June 2015}}

</ref> Hive enables developers to create their own custom functions with Java.<ref>

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==External links==

*[http://msdn2.microsoft.com/en-us/library/aa258261(SQL.80).aspx Microsoft SQL Server reference for CREATE FUNCTION]

*Visual Basic 2010 Professional/Express

*[http://dev.mysql.com/doc/refman/5.5/en/adding-functions.html MySQL manual section on UDFs]

*[http://pic.dhe.ibm.com/infocenter/db2luw/v10r5/index.jsp?topic=%2Fcom.ibm.db2.luw.sql.ref.doc%2Fdoc%2Fr0000917.html DB2 CREATE FUNCTION statement]