The D (dummy) format describes a data file column that does not map to any table column. On input (COPY FROM), a D format column describes file data to be skipped and discarded. On output (COPY INTO), a D format column describes constant data to be sent to the data file.

The column name given for any dummy column is not matched to any table column. The Dn form for COPY INTO uses the column name as the value to output; all other uses of the dummy format ignore the column name completely.