Rational Number Space is Sigma-Compact

Theorem
Let $\struct {\Q, \tau_d}$ be the rational number space under the Euclidean topology $\tau_d$.

Then $\struct {\Q, \tau_d}$ is $\sigma$-compact.

Proof
From Rational Numbers are Countably Infinite, $\Q$ is countable.

Hence the result from definition of Countable Space is $\sigma$-Compact.