performance - SQL Server - Does column order matter?

Question

In terms of performance and optimizations:

• When constructing a table in SQL Server, does it matter what order I put the columns in?
• Does it matter if my primary key is the first column?
• When constructing a multi-field index, does it matter if the columns are adjacent?
• Using ALTER TABLE syntax, is it possible to specify in what position I want to add a column?
  • If not, how can I move a column to a difference position?

Answer 1

In SQL Server 2005, placement of nullable variable length columns has a space impact - placing nullable variable size columns at the end of the definition can result in less space consumption.

SQL Server 2008 adds the "SPARSE" column feature which negates this difference.

See here.