Re: escape string type for upcoming 8.1

E'' is more a marker than a type. I realize making E a type might work,
but it seems unusual.

What we could do is backpatch E'' to 8.0.X as a no-op like it will be in
8.1.

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Jeff Davis wrote:
> >From what I've read, it looks like 8.1 will introduce the E'' escape
> string, and eventually postgresql will change the normal '' strings to
> be more SQL-compliant.
>
> If I wanted to start being forwards-compatible right now, and I have
> existing databases in 7.4 and 8.0, my idea was to create a type E. Any
> string using that type would work in 7.4/8.0 as normal, and then when I
> upgrade to 8.1 I will drop the type and the applications will still work.
>
> To do that is relatively simple, I'd just use the textin/out functions
> that already exist to create the type (which in 7.4/8.0 will give the
> desired behavior of escaping). Like so:
>
> CREATE FUNCTION ein(CSTRING) RETURNS E AS 'textin' LANGUAGE internal;
>
> CREATE FUNCTION eout(E) RETURNS CSTRING AS 'textout' LANGUAGE internal;
>
> CREATE TYPE E (input=ein,output=eout);
>
> CREATE CAST (E AS TEXT) WITHOUT FUNCTION AS IMPLICIT;
>
> CREATE CAST (TEXT AS E) WITHOUT FUNCTION AS IMPLICIT;
>
> Then, when I upgrade a system to 8.1, I can just remove the type, and
> all the applications will still work. Eventually when the '' strings are
> changed, I can start using those again, but in a SQL-compliant way.
>
> Does this migration path make sense? Will creating the type possibly
> cause casting problems of some kind? I read something about possibly
> "backpatching" the E'' string to 8.0. If someone did that, what would be
> the difference between applying a backpatch and what I did above?
>
> One thing that has me concerned about the idea is that there are some
> string constants, like B'' and X'' that aren't really types. Does that
> mean that E'' won't be a type? Why are B'' and X'' not types, and are
> there any other notations like that that are not types?
>
> Regards,
> Jeff Davis
>
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