A User-Defined Function, is a function provided by the user of a program or environment. In SQL databases, a user-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 Function Code

Below is the complete function definition:

<|/1/>CREATE <|/1/>FUNCTION dbo.udf_ListToTable
(
	@LIST 		<|/2/>NVARCHAR(<| style="color: #cc66cc;">4000),
	@DELIMITER 	<|/2/>NVARCHAR(<| style="color: #cc66cc;">10) = ','
)
<|/1/>RETURNS @ListTable <|/1/>TABLE
(
	Item <|/2/>NVARCHAR(<| style="color: #cc66cc;">200)
)
<|/1/>AS
<|/1/>BEGIN
	<|/1/>DECLARE @LenDel 	<|/2/>INT
	<|/1/>DECLARE @Pos 		<|/2/>INT
	<|/1/>DECLARE @Item 		<|/2/>NVARCHAR(<| style="color: #cc66cc;">200)
 
	--Get the length of the delimiter, use hack to get around LEN(' ') = 0 issue
	<|/1/>SET @LenDel = LEN(@DELIMITER + '|') - <| style="color: #cc66cc;">1
 
	<|/1/>SET @Pos = CHARINDEX(@DELIMITER, @LIST)
	<|/1/>WHILE @Pos > <| style="color: #cc66cc;">0
	<|/1/>BEGIN
		--Get the item
		<|/1/>SET @Item = SUBSTRING(@LIST, <| style="color: #cc66cc;">1, @Pos-<| style="color: #cc66cc;">1)
		--Add it to the table (if not empty string)
		<|/1/>IF LEN(LTRIM(@Item)) > <| style="color: #cc66cc;">0
			<|/1/>INSERT @ListTable (Item) <|/1/>VALUES (LTRIM(@Item))
		--Remove the item from the list
		<|/1/>SET @LIST = STUFF(@LIST, <| style="color: #cc66cc;">1, @Pos+@LenDel-<| style="color: #cc66cc;">1, '')
		--Get the position of the next delimiter
		<|/1/>SET @Pos = CHARINDEX(@DELIMITER, @LIST)
	<|/1/>END
 
	--Add the last item to the table (if not empty string)
	<|/1/>IF LEN(LTRIM(@LIST)) > <| style="color: #cc66cc;">0
		<|/1/>INSERT @ListTable (Item) <|/1/>VALUES (LTRIM(@LIST))
 
	<|/1/>RETURN
<|/1/>END
<|/1/>GO

The function simply loops over the list passed into the function. Each list item is then inserted into the variable named @ListTable, which is of type TABLE. The @ListTable variable is then returned out of the function and can be handled the same as any other table.

The Function In Use

A simple demonstration is as follows:

<|/1/>INSERT <|/1/>INTO tableName (column1, column2, column3, column4)
<|/1/>SELECT @variable1, @variable2, myTable.item, GETDATE()
<|/1/>FROM dbo.udf_ListToTable(@list,',') <|/1/>AS myTable

In this example, we insert the same information (@variable1, @variable2) for every instance of an item found in myTable.

This is useful, for example, if you want to apply a setting to a group of users. The group of users could be contained in a list that needs to be parsed as a table, whilst the individual setting details are contained in the other variables.

Download the Code

Download the code, rename the file to .sql and run on your database instance. You will then be able to reference the function in your Stored Procedures.

<!--- Arrays (repeat up the hierarchy) --->
<cfdump var="#arrayNew(1).getClass().getName()#">
<cfdump var="#arrayNew(1).getClass().getSuperClass().getName()#">
<!--- Structures (repeat up the hierarchy) --->
<cfdump var="#structNew().getClass().getName()#">
<cfdump var="#structNew().getClass().getSuperClass().getName()#">

What became immediately apparent was that both were handled differently. In the case of a ColdFusion array, the parent class was the java.util.Vector, which seemed obvious. The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. However, the size of a Vector can grow or shrink as needed to accommodate adding and removing items after the Vector has been created.

ColdFusion structures, however, are handled entirely differently, with the parent class being a coldfusion.runtime class. In fact, as we can see below, the code to handle a ColdFusion structure is entirely written for ColdFusion until the root class of java.lang.Object. Clearly ColdFusion does some complex wizardry to handle the complex nature of structues (associative arrays).

The class hierarchy for an Adobe ColdFusion array:

java.lang.Object
	java.util.AbstractCollection
		java.util.AbstractList
			java.util.Vector
				coldfusion.runtime.Array

The class hierarchy for an Adobe ColdFusion structure:

java.lang.Object
	coldfusion.util.CaseInsensitiveMap
		coldfusion.util.FastHashtable
			coldfusion.runtime.Struct

Being an inquisitive person, I applied the same code to Railo and BlueDragon, with equally interesting results.

The Java class hierarchy behind a Railo array:

java.lang.Object
	railo.runtime.type.ArrayImpl

The Java class hierarchy behind a Railo structure:

java.lang.Object
	railo.runtime.type.StructImpl

The Java class hierarchy behind a BlueDragon array:

java.lang.Object
	com.naryx.tagfusion.cfm.engine.cfData
		com.naryx.tagfusion.cfm.engine.cfJavaObjectData
			com.naryx.tagfusion.cfm.engine.cfArrayData
				com.naryx.tagfusion.cfm.engine.cfArrayListData

The Java class hierarchy behind a BlueDragon structure:

java.lang.Object
	com.naryx.tagfusion.cfm.engine.cfData
		com.naryx.tagfusion.cfm.engine.cfJavaObjectData
			com.naryx.tagfusion.cfm.engine.cfStructData

Adendum: Ben Nadel has a good little post on ColdFusion Data Types from Different Sources and How ColdFusion Sees Them.

Arrays and structures are also known as reference types. A reference is an object containing information which refers to data stored elsewhere, as opposed to containing the data itself. References are fundamental to constructing many data structures and in exchanging information between different parts of a program. References increase flexibility in where objects can be stored, how they are allocated, and how they are passed between areas of code. As long as we can access a reference to the data, we can access the data through it, and the data itself need not be moved. They also make sharing of data between different code areas easier; each keeps a reference to it.

Array and structure reference types are pointers to a memory space. Pointers are the most primitive and error-prone but also one of the most powerful and efficient types of references, storing only the address of an object in memory. Because arrays and structures are pointers to a space in memory, it allows for easy copying of that data. However, when copying an array or structure, there is a distinct difference between how the copy is performed. This difference relates to the concepts of shallow and deep copying.

When copying an array, a deep copy is performed by ColdFusion. This means that the data is copied and a reference to the new copy is created in memory. Therefore, following the example below, a change in the value held at position 1 of array b will not over-write the value held in position 1 of array a as they have different memory references:

<cfscript>
	a = arrayNew(1);
	a[1] = 100;
	b = a; //deep copy for Array
	b[1] = 500;
	writeOutput(a[1]); // the returned result is 100
</cfscript>

We can also use the little-known Java function equals() to demonstrate that the two arrays are not equal (the references are different).

<!---
the following returns false
a and b do not refer to the same object
 --->
<cfdump var="#a.equals(b)#">

This is not the case for a structure. When copying a structure, as in the example below, a shallow copy is performed by ColdFusion. This means that a change in b.name will also result in a change of a.name:

<cfscript>
	a = structNew();
	a.name = "Simon Whatley";
	b = a; //shallow copy for Struct
	b.name = "John Doe";
	writeOutput(a.name); // the returned result is John Doe
</cfscript>

Using the equals() method, we can show that the two structures refer to the same object:

<!---
the following returns true
a and b refer to the same object
 --->
<cfdump var="#a.equals(b)#">

However, by using the duplicate() function, a deep copy of a structure can be performed:

<cfscript>
	a = structNew();
	a.name = "Wu Mingshi";
	b = duplicate(a); //deep copy for Struct
	b.name = "Ivan Ivanovic";
	writeOutput(a.name); // the returned result is Wu Mingshi
</cfscript>

The above code results in two structures being created.

Arrays and structures although similar, behave very differently. Both are known as reference types which refer to a pointer in memory. Both have the ability to contain multiple values underneath a single variable name. Both use an index to access an individual value, but the index is numeric for arrays and a arbitrary, text value for structures. Arrays are extremely useful for numeric calculations, tabular data, and data sorting. Structures, by their nature, cannot be sorted by value, only by key name. They are commonly for related data, where order is not important and direct access to an individual element is important. Many of ColdFusion’s variable scopes (such as server, application, variables, session, form etc) can be accessed as structures.