def write_sql dbh, table
      Daru::IO.dataframe_write_sql self, dbh, table
    end
Insert each case of the Dataset on the selected table

== Arguments

* dbh - DBI database connection object.
* query - Query string.

== Usage

ds = Daru::DataFrame.new({:id=>Daru::Vector.new([1,2,3]), :name=>Daru::Vector.new(["a","b","c"])})
dbh = DBI.connect("DBI:Mysql:database:localhost", "user", "password")
ds.write_sql(dbh,"test")