To write to a database, use the structure in Tables. You can either insert new rows into the database or update rows already present. When updating, it will find the row to update by the primary key column(s) specified for the table (which is normally detected in the database import).
You can insert into or update multiple tables in the output of the map by inheriting from the structure in Tables to insert/update. Then specify the DatabaseInsert or DatabaseUpdate function as required at the root element of the Tables structure, which is the element that is the parent of the Row element.
If the representation of the output of the map is database and the output structure is a structure in Tables, it will insert into the database by default (no function is needed).