Table loading method description

When loading an R dataframe into SQL Server using write_dataframe_to_db(), the following steps are used:

1. The R dataframe is loaded into a staging table in the database in batches of n rows at a time.

2. Create target table in the database and load from staging to target.

   • If table of the specified name does NOT already exist in the database schema:

     • Create target table in the database.
       
     • Insert all rows from staging table to target table.

   • If table of same name does already exist in the database schema:

     • If argument append_to_existing = FALSE (this will result in an overwrite):
       • Drop the existing copy of the target table and create a new one.
       • Insert all rows from staging table into target table.
     • If argument append_to_existing = TRUE:
       • Check that staging table columns and existing target table columns are the same. If not, add any extra columns to existing SQL Server table.
         
       • Insert all rows from staging table into target table.

3. Delete the staging table.