Can I use the API to download a single column from a data feed?

Yes, the API may be used to download a single column from a data feed.

When using the API, please note that data on Quandl comes in two formats:  time-series and tables. You can learn more about these formats here.

Time-series

To download a single column from a time-series, use the  column_index=n parameter, like this:

https://www.quandl.com/api/v3/datasets/XNAS/ACIW.csv?column_index=4&api_key=YOURAPIKEY

The above API call will return the close column (column 4) from the XNAS/ACIW time-series because column=4. Note that column 0 is the date column and is always returned. Data begins at column 1.

To see other parameters for individual time-series, please see the documentation here. To see other examples of API calls for time-series data, please see here. 

Tables

To download a specific column from a table, use the qopts.columns= parameter, like this: 

https://www.quandl.com/api/v3/datatables/SHARADAR/SEP.csv?qopts.columns=ticker&api_key=YOURAPIKEY

The above API call will return the ticker column from SHARADAR/SEP table because qopts.columns=ticker.

To see other parameters for tables, please see the documentation here. To see other examples of API calls for tables data, please see here.