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Re: Add column if not exists (CINE)

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Cc: Kjell Rune Skaaraas <kjella79(at)yahoo(dot)no>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Add column if not exists (CINE)
Date: 2010-04-28 12:23:50
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Lists: pgsql-hackers

Takahiro Itagaki wrote:
> Kjell Rune Skaaraas <kjella79(at)yahoo(dot)no> wrote:
>> I've been reading the earlier threads at:
>> and I'm not sure I have anything that substantially new to add but:
>> I saw some indications that this might be a minority opinion,
>> well I would like to cast a vote FOR this functionality.
> +1 for CINE, just because MySQL supports it.

MySQL compatibility has never been our aim. We should adopt ideas from 
other projects because they are good, not just because they are there.

That doesn't mean I don't think this is a good idea.

> But before developing, we need to decide how to handle an added object
> that has the same name but has different definitions. 

The OP explicitly stated that in his opinion nothing should be done in 
such cases. That's a defensible position, in the case of objects such as 
tables that must be unique by name (e.g. tables).  But what would we do 
about objects where the name could be overloaded? Since we would 
presumably want to do this for all (or almost all) of our CREATE/ADD 
commands, we'd need a policy on those.
> Also, developers should consider not only ADD COLUMN but also other
> CREATE or ADD commands. The patch will be large, including documentation
> adjustments in many places -- it would be hard work.

I can speak with some experience on this at least. :-) I don't see that 
it would be a heck of a lot bigger than the DROP IF EXISTS cases, which 
after the first few had been done were not hard, merely tedious to do :-)



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