ERROR: Port ... prevents drop of column ...

Reason:

You attempted to drop a column using drop_column() but that column is used by a port.

Resolution:

Drop the port first. You may also have to drop sources attached to the port and terminate any agent processes using those sources.

Tips:

• Use the star$ports view to see which ports use the table and which columns they are configured for.
• Use the star$sources view to see which sources are attached to ports.