Define a variable in two ranges

Is there anyway i can define a JuMP variable in two different ranges?

Say the first range is between 3:6 and the second one between 9:12.

No. But you can write a reformulation like:

@variable(model, range_variable)
x = @variable(model, [1:2])
z = @variable(model, [1:2], Bin)
@constraints(model, begin
    3z[1] <= x[1]
             x[1] <=  6z[1]
    9z[2] <= x[2]
             x[2] <= 12z[2]
    z[1] + z[2] == 1
    range_variable == x[1] + x[2]

Thank you for the tip! I’m going to try that!