Re: COPY IN as SELECT target

Andrew Dunstan <andrew@dunslane.net> writes:
> Tom Lane wrote:
>> The problem with COPY FROM is that it hard-wires a decision that there
>> is one and only one possible result format, which I think we pretty
>> much proved already is the wrong thing.  I'm not thrilled with "RETURNING
>> ARRAY" either, but we need to leave ourselves wiggle room to have more
>> than one result format from the same source file.

> Well, we could have "RETURNING type-expression" with  "text[]" supported 
> for the first iteration.

> In answer to Heiki's argument, what I wanted was exactly to return an 
> array of text for each row. Whatever we have needs to be able to handle 
> to possibility of ragged input (see previous discussion) so we can't tie 
> it down too tightly.

I think that there are two likely possibilities for the result format:

* "Raw" data after just the de-escaping and column separation steps.
Array of text is probably the right thing here, at least for a text COPY
(doesn't seem to cover the binary case though).

* The data converted to some specified row type.

"RETURNING type-expression" is probably not good since it looks more
like the second case than the first --- and in fact it could be outright
ambiguous, what if your data actually is one column that is a text
array?

If we're willing to assume these are the *only* possibilities then we
could use "COPY FROM ..." for the first and "COPY RETURNING type-list
FROM ..." for the second.  I'm a bit uncomfortable with that assumption
though; it seems likely that we'll want to shoehorn in some more
alternatives later.  (Like, what about the binary case?)
        regards, tom lane