I have beeing reading the doc and I can
did not understand your question. Do you want to store the data from an external RDBMS into Tamino or to another ext.DB?
I have a relational database and I want to load all the data in the Tamino. I wonder if there is any automatic tool to do this.
no, there is no automatic tool, but you can use the X-Node to access the RDBMS (as far as your specific DB is supported) and then store data in Tamino.
For detailed information about X-Node, please refer the Tamino documentation.