Re: Bug in MergeAttributesIntoExisting() function.

Hi,

On Mon, Jan 4, 2016 at 8:11 PM, amul sul <sul_amul@yahoo.co.in> wrote:
> Hi,
>
> In inheritance, child column's pg_attribute.attislocal flag not getting updated, if it is inherited using ALTER TABLE
<child>INHERIT <parent>.
 
>
> Due to this, if we try to drop column(s) from parent table, which are not getting drop from child.
> Attached herewith is quick patch fixing this issue.
>
>
> ----------------------Demonstration:
> ----------------------
> CREATE TABLE p1 (a int , b int, c int, d int);
>
> CREATE TABLE c1 () inherits (p1);CREATE TABLE c2 (a int , b int, c int, d int);
>
>
> --Drop parent's column
> ALTER TABLE p1 DROP COLUMN b;
> ALTER TABLE p1 DROP COLUMN c;
> ALTER TABLE p1 DROP COLUMN d;
>
>
> postgres=# \d p1
>       Table "public.p1"
>  Column |  Type   | Modifiers
> --------+---------+-----------
>  a      | integer |
> Number of child tables: 2 (Use \d+ to list them.)
>
> postgres=# \d c1
>       Table "public.c1"
>  Column |  Type   | Modifiers
> --------+---------+-----------
>  a      | integer |
> Inherits: p1
>
> postgres=# \d c2
>       Table "public.c2"
>  Column |  Type   | Modifiers
> --------+---------+-----------
>  a      | integer |
>  b      | integer |
>  c      | integer |
>  d      | integer |
> Inherits: p1
>
>
> ----------------------
> You can see columns are not dropped from child c2 table, which we have inherited using ALTER command.

I'm afraid the patched behavior of MergeAttributeIntoExisting() would
be inconsistent with MergeAttributes(). For example, try with the
following:

CREATE TABLE c1(b int) INHERITS(p1);

In this case, MergeAttributes() would cause 'b' to be defined to be a
local attribute (ie, with attislocal = true) and hence would not be
dropped unlike c2 which the patched behavior would cause to be
dropped.

Am I missing something?

Thanks,
Amit