问题1：很多时候是引用的问题
UndefVarError: dataset not defined
top-level scope at JuliaDBTest:50Pkg
Pkg.add("dataset ")
问题2：错误：
UndefVarError: groupby not defined
top-level scope at JuliaDBTest:49
或者告警：
WARNING: both RDatasets and JuliaDB export "groupby"; uses of it in module Main must be qualified
解决方法：通过import指定模块的函数
import JuliaDB: pkeynames, pkeys, excludecols, select, transform，groupby
问题3：WARNING: could not import DataFramesMeta.@groupby into Main
解决方法：
去掉@符号用 groupby