Re: [BUG?] strange behavior in ALTER TABLE ... RENAME TO on inherited columns - Mailing list pgsql-hackers

Tom Lane wrote:
> Thom Brown <thombrown@gmail.com> writes:
>> 2009/11/4 Alvaro Herrera <alvherre@commandprompt.com>:
>>> KaiGai Kohei wrote:
>>>> I think we should not allow to rename a column with attinhcount > 1.
>
>>> I think we should fix ALTER TABLE to cope with multiple inheritance.
>
>> I'd be interested to see how this should work.
>
> Yeah.  I don't think a "fix" is possible, because there is no
> non-astonishing way for it to behave.  I think KaiGai is right that
> forbidding the rename is the best solution.

The attached patch forbids rename when the attribute is inherited
from multiple parents.

  postgres=# CREATE TABLE t1 (a int, b int);
  CREATE TABLE
  postgres=# CREATE TABLE t2 (b int, c int);
  CREATE TABLE
  postgres=# CREATE TABLE t3 (d int) INHERITS (t1, t2);
  NOTICE:  merging multiple inherited definitions of column "b"
  CREATE TABLE
  postgres=# SELECT * FROM t3;
   a | b | c | d
  ---+---+---+---
  (0 rows)

  postgres=# ALTER TABLE t1 RENAME b TO x;
  ERROR:  cannot rename multiple inherited column "b"


The regression test detected a matter in the misc test.

It tries to rename column "a" of "a_star" table, but it failed due to
the new restriction.

  --
  -- test the "star" operators a bit more thoroughly -- this time,
  -- throw in lots of NULL fields...
  --
  -- a is the type root
  -- b and c inherit from a (one-level single inheritance)
  -- d inherits from b and c (two-level multiple inheritance)
  -- e inherits from c (two-level single inheritance)
  -- f inherits from e (three-level single inheritance)
  --
  CREATE TABLE a_star (
      class       char,
      a           int4
  );

  CREATE TABLE b_star (
      b           text
  ) INHERITS (a_star);

  CREATE TABLE c_star (
      c           name
  ) INHERITS (a_star);

  CREATE TABLE d_star (
      d           float8
  ) INHERITS (b_star, c_star);

At the misc test,

  --- 242,278 ----
    ALTER TABLE c_star* RENAME COLUMN c TO cc;
    ALTER TABLE b_star* RENAME COLUMN b TO bb;
    ALTER TABLE a_star* RENAME COLUMN a TO aa;
  + ERROR:  cannot rename multiple inherited column "a"
    SELECT class, aa
       FROM a_star* x
       WHERE aa ISNULL;
  ! ERROR:  column "aa" does not exist
  ! LINE 1: SELECT class, aa
  !

It seems to me it is a case the regression test to be fixed up.
(We don't have any reasonable way to know whether a certain attribute
has a same source, or not.)

Any comments?
--
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai@ak.jp.nec.com>
Index: src/test/regress/sql/inherit.sql
===================================================================
*** src/test/regress/sql/inherit.sql    (revision 2388)
--- src/test/regress/sql/inherit.sql    (working copy)
*************** CREATE TABLE inh_error1 () INHERITS (t1,
*** 336,338 ****
--- 336,352 ----
  CREATE TABLE inh_error2 (LIKE t4 INCLUDING STORAGE) INHERITS (t1);

  DROP TABLE t1, t2, t3, t4, t12_storage, t12_comments, t1_inh, t13_inh, t13_like, t_all;
+
+ -- Test for renaming
+ CREATE TABLE t1 (a int, b int);
+ CREATE TABLE t2 (b int, c int);
+ CREATE TABLE t3 (d int) INHERITS(t1, t2);
+ ALTER TABLE t1 RENAME a TO x;
+ ALTER TABLE t1 RENAME b TO y;    -- to be failed
+ ALTER TABLE t3 RENAME d TO z;
+ SELECT * FROM t3;
+ DROP TABLE t3;
+ DROP TABLE t2;
+ DROP TABLE t1;
+
+
Index: src/test/regress/expected/inherit.out
===================================================================
*** src/test/regress/expected/inherit.out    (revision 2388)
--- src/test/regress/expected/inherit.out    (working copy)
*************** NOTICE:  merging column "a" with inherit
*** 1057,1059 ****
--- 1057,1076 ----
  ERROR:  column "a" has a storage parameter conflict
  DETAIL:  MAIN versus EXTENDED
  DROP TABLE t1, t2, t3, t4, t12_storage, t12_comments, t1_inh, t13_inh, t13_like, t_all;
+ -- Test for renaming
+ CREATE TABLE t1 (a int, b int);
+ CREATE TABLE t2 (b int, c int);
+ CREATE TABLE t3 (d int) INHERITS(t1, t2);
+ NOTICE:  merging multiple inherited definitions of column "b"
+ ALTER TABLE t1 RENAME a TO x;
+ ALTER TABLE t1 RENAME b TO y;    -- to be failed
+ ERROR:  cannot rename multiple inherited column "b"
+ ALTER TABLE t3 RENAME d TO z;
+ SELECT * FROM t3;
+  x | b | c | z
+ ---+---+---+---
+ (0 rows)
+
+ DROP TABLE t3;
+ DROP TABLE t2;
+ DROP TABLE t1;
Index: src/backend/commands/tablecmds.c
===================================================================
*** src/backend/commands/tablecmds.c    (revision 2388)
--- src/backend/commands/tablecmds.c    (working copy)
*************** renameatt(Oid myrelid,
*** 2024,2029 ****
--- 2024,2040 ----
                   errmsg("cannot rename inherited column \"%s\"",
                          oldattname)));

+     /*
+      * If the attribute is inherited from multiple parents, forbid
+      * the renaming, because we don't have any reasonable way to keep
+      * integrity in whole of the inheritance relationship.
+      */
+     if (attform->attinhcount > 1)
+         ereport(ERROR,
+                 (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+                  (errmsg("cannot rename multiple inherited column \"%s\"",
+                          oldattname))));
+
      /* should not already exist */
      /* this test is deliberately not attisdropped-aware */
      if (SearchSysCacheExists(ATTNAME,