Обсуждение: array manipulations

Hi all again,

Tom, _thanks_ for information! I really appreciated it. I managed to
create a function which can be used to append or delete elems in an
integer array. I needed it because I wanted to somehow solve the
user-group relationship problems with Postgres.

If you are interested, I could extend its functionality to other types
as well and send this small pack to you. For this, however I should know
more about how Postgres manages types internally...

Regards,
Peter Blazso

Peter Blazso <blazso@deltav.hu> writes:
> If you are interested, I could extend its functionality to other types
> as well and send this small pack to you. For this, however I should know
> more about how Postgres manages types internally...

I think it should be possible to make a type-independent version of that
code, and if you want to do so it'd be a great extension.

How does it look to the user?  Something like
UPDATE table SET arrayfield = arrayInsert(arrayfield, index, newval)
UPDATE table SET arrayfield = arrayDelete(arrayfield, index)

I suppose?  What do you do about multi-dimensional arrays?

One thing a number of people have complained about is that the natural
way to extend an array is
UPDATE table SET arrayfield[n+1] = newval

if arrayfield currently has n entries.  The array assignment code ought
to handle this case but doesn't.  I don't think it would be a huge fix
but I haven't looked at the code enough to understand what would need
to change.
        regards, tom lane

Tom Lane wrote:

> I think it should be possible to make a type-independent version of that
> code, and if you want to do so it'd be a great extension.

I should have much more spare time but I'll try... :-)

> How does it look to the user?  Something like
>
>         UPDATE table SET arrayfield = arrayInsert(arrayfield, index, newval)
>         UPDATE table SET arrayfield = arrayDelete(arrayfield, index)

Not exactly. My functions don't use indices yet and they still work only on one
dimensional 'int' arrays. You can insert a new value only as the last elem and
delete all values from the array that match a given integer. They can be used
like below:
       UPDATE table SET arrayfield = array_app_int(arrayfield, newval);       UPDATE table SET arrayfield =
array_del_int(arrayfield,matchval);
 

This time I focused only on user additions/deletions to/from a group in
'pg_group', however the code can be extended easily to do other things as well.

> What do you do about multi-dimensional arrays?

Unfortunately nothing, yet. This code is still an intro into array
manipulations.

> One thing a number of people have complained about is that the natural
> way to extend an array is
>
>         UPDATE table SET arrayfield[n+1] = newval
>
> if arrayfield currently has n entries.  The array assignment code ought
> to handle this case but doesn't.  I don't think it would be a huge fix
> but I haven't looked at the code enough to understand what would need
> to change.

If you want I can send you these functions accompanied by some notes and
comments I just did ...

Peter Blazso