Well,the function states that build a date given the various parts like year, month and day. We have already seen this function in dotnet. Out of the various overloaded constructor of DateTime struct, we have

public DateTime(int year, int month, int day);

So if we write

Console.WriteLine(new DateTime(2011, 7, 23));

The output will be: 7/23/2011 12:00:00 AM

Now we have the same opportunity to do from Sql Server with the help of DateFromParts.

Purpose: Returns a date given its parts like year, month, day.

Syntax: DateFromParts(year,month,day)

Where,

Year => the year value

Month => the month value

Day => Day value.

Example 1: Simple example

Select DateFromParts(2011,7,23) [Result]

/*
	Result
	------
	2011-07-23
*/

Example 2: Specifying all nulls

Select DateFromParts(null,null,null) [Result]

/*
	Result
	------
	 Null
*/

Example 3: Omitting mandatory fields will raise exception

Select DateFromParts(2011,23) [Result]

Msg 174, Level 15, State1, Line1
The datefromparts function requires 3 argument(s)

Example 4: Inserting value 2 for all the fields

Select DateFromParts(2,2,2) [Result]

/*
	 Result
	 ------
	 0002-02-02
*/

Hope this helps