Russell Smith wrote:
Tom Lane wrote:
Stephen Frost <[EMAIL PROTECTED]> writes:
Force references to go through macros which implement the lookup for the
appropriate type?  ie: LOGICAL_COL(table_oid,2) vs.
PHYSICAL_COL(table_oid,1)  Perhaps that's too simplistic.

It doesn't really address the question of how you know which one to
use at any particular line of code; or even more to the point, what
mechanism will warn you if you use the wrong one.

My gut feeling about this is that we could probably enforce such a
distinction if we were using C++, but while coding in C I have no
confidence in it.  (And no, that's not a vote to move to C++ ...)
What about a comprimise...

The 8.1 documentation for ALTER TABLE states the following.

Adding a column with a non-null default or changing the type of an existing column will require the entire table to be rewritten. This may take a significant amount of time for a large table; and it will temporarily require double the disk space.

Now, we are rewriting the table from scratch anyway, the on disk format is changing. What is stopping us from switching the column order at the same time. The only thing I can think is that the catalogs will need more work to update them. It's a middle sized price to pay for being able to reorder the columns in the table. One of the problems I have is wanting to add a column in the middle of the table, but FK constraints stop me dropping the table to do the reorder. If ALTER TABLE would let me stick it in the middle and rewrite the table on disk, I wouldn't care. It's likely that I would be rewriting the table anyway. And by specifying AT POSITION, or BEFORE/AFTER you know for big tables it's going to take a while.

This isn't really a compromise. Remember that this discussion started with consideration of optimal record layout (minimising space use by reducing or eliminating alignment padding). The above proposal really does nothing for that.



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