Re: [HACKERS] Bug in DROP NOT NULL

Thu, 31 Mar 2005 05:03:09 -0800

Sorry, was in a rush before. I still don't have time to fix this for 8.0.2, so that's why I rushed out the report. Here is a full description...

You can drop a NOT NULL on a column, even if that column is part of an index that is clustered, where the index does not index NULLs. 

First, install tsearch2...

test=# create table test (a tsvector);
CREATE TABLE
test=# create index test_gist_idx on test using gist (a);
CREATE INDEX
test=# \d test
      Table "public.test"
 Column |   Type   | Modifiers
--------+----------+-----------
 a      | tsvector |
Indexes:
    "test_gist_idx" gist (a)

test=# cluster test_gist_idx on test;
ERROR:  cannot cluster when index access method does not handle null values
HINT:  You may be able to work around this by marking column "a" NOT NULL.
test=# alter table test alter a set not null;
ALTER TABLE
test=# cluster test_gist_idx on test;
CLUSTER
test=# \d test
      Table "public.test"
 Column |   Type   | Modifiers
--------+----------+-----------
 a      | tsvector | not null
Indexes:
    "test_gist_idx" gist (a) CLUSTER

test=# alter table test alter a drop not null;
ALTER TABLE
test=# cluster test_gist_idx on test;
ERROR:  cannot cluster when index access method does not handle null values
HINT:  You may be able to work around this by marking column "a" NOT NULL.
test=# \d test
      Table "public.test"
 Column |   Type   | Modifiers
--------+----------+-----------
 a      | tsvector |
Indexes:
    "test_gist_idx" gist (a) CLUSTER

Note that index is still 'clustered', but unclusterable.

The correct behaviour IMHO is to prevent dropping NOT NULL on a column that particpates in such an index. (Index access method that does not handle nulls)

Also, I dont think that ALTER TABLE blah CLUSTER ON foo; actually warns about clustering a non-null indexing index. However, CLUSTER foo ON blah; does. 

I was wrong about that...

Chris

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