User Defined Procedure (UDP)

A type of User-Defined Routine that accepts zero or more parameters but does not return a value. SQLstream allows the creation of C++, Java or SQL procedures.

The following describes the differences between user-defined functions, procedures, and transforms:

User-Defined Function (UDF)

A UDF is used in a scalar expression; it takes (0 .. n) scalar arguments and returns a scalar value. When used in a query, a scalar expression is evaluated for each row.

  • Inputs: Zero or more parameters
  • Returns: A single scalar value
  • SQL: CREATE FUNCTION

User-Defined Procedure (UDP)

A UDP is just a UDF that returns no value; it is evaluated for a side effect.

  • Inputs: Zero or more parameters
  • Returns: No values are returned
  • SQL: CREATE PROCEDURE

User-Defined Transform (UDX)

A [UDX](/glossary/userdefinedtransform] is different: its output is a stream (or table) of rows, and its inputs can either be scalars, streams or tables. In SQL, a streaming argument to a UDX is represented as CURSOR(SELECT STREAM ... FROM ...) and a scalar is represented by any scalar expression.

The invocation of a UDX is quite often preceded by the keyword STREAM (for a streaming UDX) or TABLE (for a finite UDX). For example:

SELECT STREAM *
 FROM STREAM(
  filterSignal( CURSOR( SELECT STREAM * FROM "RawSignals")));