Port Bug Report: Query processing seems broken

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Joerg Fischer
Your email address : fischer(at)zkm(dot)de

Category : runtime: back-end: SQL
Severity : serious

Summary: Query processing seems broken

System Configuration
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Operating System : SuSE Linux 6.0 (i386) - Kernel 2.0.36 (ELF)

PostgreSQL version : 6.5beta1

Compiler used : egcs-2.91.60

Hardware:
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Pentium II-450, 128 MB RAM, 9 GB U2W HD, Adaptec U2W Cont.

Linux salon09 2.0.36 #3 Mon Apr 26 20:44:52 CEST 1999 i686 unknown

Versions of other tools:
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Problem Description:
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Test Case:
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The following query fails with PGSQL 6.5beta1,
even though it seems correct:

select superext as name from OM_ExtendInheritance where subext in (
select superext as name from OM_ExtendInheritance where subext in (
select 'Patient' as name
)
union select 'Patient' as name
);

Postgresql reports:
ERROR: parser: parse error at or near "union"

Could there be a problem handling nested expressions?

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Solution:
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