The question I had, was not the XOR swap but the following,

When I write “Select @variable1 =… ,  @variable2 =@variable1 + … ;”

How is it possible that the result  @variable1 is used for computation of @variable2

I expected this, but it strike me as odd.

Second question I had was the following

When the “select” command is used for variables.  Is @variable2 or @variable1 first calculated.