Thread: BUG #2112: query kills db thread

The following bug has been logged online:

Bug reference:      2112
Logged by:          Jim Dew
Email address:      jdew@yggdrasil.ca
PostgreSQL version: 8.1.0
Operating system:   OpenBSD
Description:        query kills db thread
Details:

Stumbled upon a (broken) query that causes the 8.1.0 thread handling the
query to die:

select foo from (select null) as foo

Now, this query just produces an error on 8.0.3

8.1.0:

Welcome to psql 8.1.0, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

suth=# select foo from (select null) as foo;
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>


8.0.3:
Welcome to psql 8.0.3, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

suth=# select foo from (select null) as foo;
ERROR:  subquery foo does not have attribute 0
suth=#

"Jim Dew" <jdew@yggdrasil.ca> writes:
> Stumbled upon a (broken) query that causes the 8.1.0 thread handling the
> query to die:
> select foo from (select null) as foo

Confirmed here --- will look into it.  Thanks for the report!

> Now, this query just produces an error on 8.0.3

However, there's something rotten in the state of Denmark in 8.0 too:

regression=# select foo from (select null) as foo;
ERROR:  subquery foo does not have attribute 0

7.4 gives what I'd consider a reasonable error message:

regression=# select foo from (select null) as foo;
ERROR:  relation reference "foo" cannot be used as a select-list entry
HINT:  Write "foo".* to denote all the columns of the relation.

Maybe we need a regression test to exercise this case, because it seems
we've been backsliding on this rather badly ...

            regards, tom lane

"Jim Dew" <jdew@yggdrasil.ca> writes:
> Stumbled upon a (broken) query that causes the 8.1.0 thread handling the
> query to die:
> select foo from (select null) as foo

Fixed in 8.0 and up.  If you need the patch for 8.1, it's pretty simple:

Index: src/backend/executor/execQual.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/execQual.c,v
retrieving revision 1.183.2.1
diff -c -r1.183.2.1 execQual.c
*** src/backend/executor/execQual.c    22 Nov 2005 18:23:08 -0000    1.183.2.1
--- src/backend/executor/execQual.c    14 Dec 2005 16:25:05 -0000
***************
*** 541,547 ****
      Assert(variable->varno != OUTER);
      slot = econtext->ecxt_scantuple;

!     tuple = slot->tts_tuple;
      tupleDesc = slot->tts_tupleDescriptor;

      /*
--- 541,547 ----
      Assert(variable->varno != OUTER);
      slot = econtext->ecxt_scantuple;

!     tuple = ExecFetchSlotTuple(slot);
      tupleDesc = slot->tts_tupleDescriptor;

      /*

Thanks for the report!

            regards, tom lane