public static <T> WindowOver<T> nthValue(Expression<T> expr, Number n) {
        return nthValue(expr, ConstantImpl.create(n));
    }
NTH_VALUE returns the expr value of the nth row in the window defined by the analytic clause.
The returned value has the data type of the expr.

@param expr measure expression
@param n one based row index
@return nth_value(expr, n)
querydsl-sql/src/main/java/com/querydsl/sql/SQLExpressions.java