> 
> Never, unless you drop and recreate the table.  Removing a dropped
> column would change the attnums of following columns, which we
> can't support because the tableoid+attnum is the only persistent
> identifier of a column.
> 
> (From memory, operations like VACUUM FULL and CLUSTER will rewrite
> dropped columns with NULLs to reduce their storage impact.  But they
> don't go away.)
> 
> 

Thank you.  I remember reading it here that VACUUM FULL does what you describe 
above.
So even TRUNCATE does not help here?



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