PostgresSQL 7.1.3 not parsing SELECT portion of SQL correctly

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Mark Jeacocke
Your email address : mbj(at)ezytools(dot)com

System Configuration
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Architecture (example: Intel Pentium) : AMD Athlon XP 1600

Operating System (example: Linux 2.0.26 ELF) : RedHat Linux 7.0 Kernel
2.4.2

PostgreSQL version (example: PostgreSQL-7.1.3): PostgreSQL-7.1.3

Compiler used (example: gcc 2.95.2) : Downloaded offical RPMS from
Postgres mirror

Please enter a FULL description of your problem:
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Seems to be a parsing problem in the select portion of the SQL statement:

select DISTINCT TABLEID, '' AS ALIAS from TABLE; :FAILS
select DISTINCT TABLEID, 'test' AS ALIAS from TABLE; :FAILS
select DISTINCT TABLEID, Null AS ALIAS from TABLE; :FAILS
select DISTINCT TABLEID, trim('') AS ALIAS from TABLE; :SUCCEEDS
select DISTINCT TABLEID, 2 AS ALIAS from TABLE; :SUCCEEDS

I believe all five queries should succeed.

Please describe a way to repeat the problem. Please try to provide a
concise reproducible example, if at all possible:
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See above.

If you know how this problem might be fixed, list the solution below:
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