bug in information_schema?
Found this in 7.4.5, verified it's still in 8.0b4:
test=> select * from information_schema.referential_constraints;
test|public|$1|test|public|reftest1_pkey|NONE|NO ACTION|CASCADE
test|public|$1|test|public|reftest1_pkey|NONE|NO ACTION|NO ACTION
test|public|$1|test|public|reftest1_pkey|NONE|NO ACTION|NO ACTION
In that case there are three tables all referencing the same column of a
fourth - but there is no way at all to tell which row corresponds to which
table, and hence no way to join against, say, table_constraints.
A similar issue may exist with the check_constraints view, which was the
only other place I found where constraint_name is used without any table
name being present. I don't know what the spec says, but it seems that
something is assuming that constraint_name is unique within the schema,
which of course is not the case in the above example.
--
Andrew, Supernews
http://www.supernews.com - individual and corporate NNTP services
On Sat, 27 Nov 2004 14:24:40 +0000, Andrew - Supernews wrote:
A similar issue may exist with the check_constraints view, which was the
only other place I found where constraint_name is used without any table
name being present. I don't know what the spec says, but it seems that
something is assuming that constraint_name is unique within the schema,
which of course is not the case in the above example.
It has been discussed elsewhere some months ago:
http://thread.gmane.org/gmane.comp.db.postgresql.sql/11397
The problem makes the INFORMATION_SCHEMA rather useless for some kinds of
queries, like you have shown. However, I don't believe that schema-unique
constraint names will be an option any time soon, due to backwards
compatibility :-(
--
Greetings from Troels Arvin, Copenhagen, Denmark
Troels Arvin <troels@arvin.dk> writes:
On Sat, 27 Nov 2004 14:24:40 +0000, Andrew - Supernews wrote:
something is assuming that constraint_name is unique within the schema,
which of course is not the case in the above example.
The problem makes the INFORMATION_SCHEMA rather useless for some kinds of
queries, like you have shown. However, I don't believe that schema-unique
constraint names will be an option any time soon, due to backwards
compatibility :-(
We have changed 8.0 to ensure that automatically-generated constraint
names are unique across a schema. I doubt we will ever enforce that
against user-specified names, though. If you want to use the
information schema to trace constraints, you'll have to impose that
discipline on yourself.
regards, tom lane