how to comment a column and how to remove a comment from a column
Create Comment
COMMENT ON < SCHEMA >.< TABLE > ( IS '< this is a comment >')
Update Comment
Use the same command to define a new comment at the same column
COMMENT ON < SCHEMA >.< TABLE > ( IS '< this is a comment >')
Remove Comment(Put two simple quotes without space)
COMMENT ON < SCHEMA >.< TABLE > ( IS '')