Re: ALTER TABLE modifications - Mailing list pgsql-patches

Is this to be applied to CVS HEAD?

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Rod Taylor wrote:
> A general re-organization of Alter Table. Node wise, it is a
> AlterTableStmt with a list of AlterTableCmds.  The Cmds are the
> individual actions to be completed (Add constraint, drop constraint, add
> column, etc.)
>
> Processing is done in 2 phases. The first phase updates the system
> catalogs and creates a work queue for the table scan. The second phase
> is to conduct the actual table scan evaluating all constraints and other
> per tuple processing simultaneously, as required. This has no effect on
> single step operations, but has a large benefit for combinational logic
> where multiple table scans would otherwise be required.
>
> Steps for the table scan include expression processing (default or
> transform expressions), not null constraint process, other constraints.
>
>
> The code has been simplified a little. Simple permission and recursion
> checks are conducted in the common area and an enum for the command type
> is used rather than a Char.
>
>
> ALTER TABLE ADD COLUMN col DEFAULT 3 NOT NULL;
>         Allow creation of a column with a default (filled) and not null
>         constraint. This is internally subdivided into 3 actions much
>         like the below syntax.
>
> ALTER TABLE tab ADD COLUMN col DEFAULT 3, ADD CHECK (anothercol > 3);
>         The above combinational syntax is commented out in gram.y. The
>         support framework is used in both the above and below items, but
>         arbitrary statements probably have some issues -- I've not
>         tested enough to determine.
>
>         If it is useful, it will be submitted at a later date.
>
> ALTER TABLE tab ALTER COLUMN col TYPE text TRANSFORM ...;
>         Currently migrates indexes, check constraints, defaults, and the
>         column definition to the new type with optional transform. If
>         the tranform is not supplied, a standard assignment cast is
>         attempted.
>
>         One issue is that it detects dependencies way too late in the
>         game (after the TRANFORM has been applied). I tried mucking up
>         performDeletion to have a RESTRICT that did not throw the error
>         at the end (or physically remove the items) but that didn't work
>         out. Any bright ideas on how to achieve the NOTICES from a
>         failed DROP COLUMN earlier? Otherwise, I can put in single
>         object detection at that point.
>
>         It does not migrate foreign keys yet (should be easy to add) and
>         will be forwarded as an independent patch at a later time.
>         Currently foreign keys are rejected like views, functions, etc.
>
>
> Comments appreciated.
> --
> Rod Taylor <pg [at] rbt [dot] ca>
>
> Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL

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