我曾经go build生成文件。但是我只能生成main，这意味着什么都不生成就可以go build main.go工作go builddao.go？
go build
main
go build main.go
go builddao.go
我如何产生dao？
dao
来自go help build：
go help build
When the command line specifies a single main package, build writes the resulting executable to output. Otherwise build compiles the packages but discards the results, serving only as a check that the packages can be built.
