Re: Add column with If Not Exists

On 08/04/2018 08:56 AM, Simon White wrote:
> Hi
>
> I would like to suggest the addition of the "If not exists" to the Add
> Column feature of Postgres.  There are quite common situations where
> ensuring a column exists is important so that an update to remote
> devices will not fail but it is not so important that deprecated fields
> be removed.  This is often the case with backward compatibility.  New
> columns will not affect old systems but allows all remote devices
> running older software to be updated using the same process as new
> devices.  Once the hardware reaches end of life it will be replaced and
> the new hardware will use the new columns.  So having the ability to
> Alter the table with a series of Add Column commands ensures that the
> new records included in the update are added to the table.  Having the
> "if not exists" would remove all of this potential complexity and allows
> a quick and easy method to ensure the column exists in the table using
> simple SQL commands that will not cause errors if the column is already
> present.

Sort of like this:

https://www.postgresql.org/docs/9.6/static/sql-altertable.html

"ADD [ COLUMN ] [ IF NOT EXISTS ] ..."

in 9.6+

>
> I understand that some people will feel this is not the recommended way
> to proceed.  I understand there are lots of ways this can be handled
> differently as I have been working with database of various kinds for
> over 30 years.  All I am suggesting is that this feature would be nice
> to have in some scenarios and thus would like it considered.  I do not
> wish to start a discussion on whether using it is a sound approach or
> not as that is a different discussion.
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com