Multiply values of a column.

Multiplying with coalesce. its quite simple but I get values in a column multiplied...

declare @MyTable table (col int)

Insert into @MyTable values (1)
Insert into @MyTable values (2)
Insert into @MyTable values (3)
Insert into @MyTable values (4)
Insert into @MyTable values (5)

declare @a int
select @a = col*coalesce(@a,col) from @MyTable
select @a