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.klaver@aklaver.com