From MSDN:

Segment http://msdn.microsoft.com/en-us/library/ms180774(v=SQL.100).aspx] is a physical and a logical operator. It divides the input set into segments based on the value of one or more columns. These columns are shown as arguments in the Segment operator. The operator then outputs one segment at a time.

The Sequence Project http://msdn.microsoft.com/en-us/library/ms187041(v=SQL.100).aspx] operator adds columns to perform computations over an ordered set. It divides the input set into segments based on the value of one or more columns. The operator then outputs one segment at a time. These columns are shown as arguments in the Sequence Project operator.

Microsoft SQL Server supports four types of functions: RANK, DENSE_RANK, ROW_NUMBER, and NTILE. Sequence Project will generate plans that have a Sequence Project and generally two segments.

Sequence Project is a physical and a logical operator.

Yeah, I know, it helps a lot 😀

Jan Studenovsky