Let $F:=\{f\in\mathbb{F}_q[X_1,\ldots,X_n]: \textrm{deg}(f)\leq d\}$ be the set containing all $n$-variate polynomials of degree less than or equal to $d$ over finite field $\mathbb{F}_q$ of prime power $q$. Suppose that $f$ is chosen uniformly at random from $F$ and let $N(f)$ be the number of distinct roots of $f$ in $\mathbb{F}_q$, namely $N(f)=\#\{(x_1,\ldots,x_n)\in\mathbb{F}_q^n:f(x_1,\ldots,x_n)=0\}$. I am interested in (the upper bound of) the $m$-th moment $\mathbb{E}[(N(f))^m]$ for $m\geq 1$.
By Schwartz–Zippel lemma, there is an upper bound $\mathbb{E}[(N(f))^m]\leq (dq^{n-1})^m$. Is this the best possible upper bound?