Thread: undocumented feature or bug in subquery : psql (PostgreSQL) 9.4.6 on SLES12 SP1

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Page: https://www.postgresql.org/docs/9.4/static/functions-subquery.html
Description:

psql (PostgreSQL) 9.4.6 on SLES12 SP1
2 tables a and b
               Table "public.a"
     Column      |           Type           |   Modifiers
-----------------+--------------------------+---------------
 foo             | integer                  | not null
 bar             | integer                  | not null

               Table "public.b"
     Column      |           Type           |   Modifiers
-----------------+--------------------------+---------------
 bar             | integer                  | not null

No error when executing this statement even though table b does not contain
column foo
SELECT foo,bar FROM a WHERE foo=1 AND bar NOT IN (SELECT bar FROM b WHERE
bar > 2 AND foo=2)

Get an error on this one ERROR:  column b.foo does not exist
SELECT foo,bar FROM a WHERE foo=1 AND bar NOT IN (SELECT bar FROM b WHERE
b.bar > 2 AND b.foo=2)

It works if I remove foo from the subquery.
SELECT foo,bar FROM a WHERE foo=1 AND bar NOT IN (SELECT bar FROM b WHERE
b.bar > 2)

Do I need to qualify all columns in the subquery or is this a bug is psql
9.4.6?

otter117@yahoo.de writes:
> 2 tables a and b
>                Table "public.a"
>      Column      |           Type           |   Modifiers
> -----------------+--------------------------+---------------
>  foo             | integer                  | not null
>  bar             | integer                  | not null

>                Table "public.b"
>      Column      |           Type           |   Modifiers
> -----------------+--------------------------+---------------
>  bar             | integer                  | not null

> No error when executing this statement even though table b does not contain
> column foo
> SELECT foo,bar FROM a WHERE foo=1 AND bar NOT IN (SELECT bar FROM b WHERE
> bar > 2 AND foo=2)

No, but table a does, and that's a legal outer reference per the SQL
standard.  This is neither a bug nor undocumented.

> Do I need to qualify all columns in the subquery or is this a bug is psql
> 9.4.6?

It's often wise to qualify column references in multi-table queries
(subqueries or not) to ensure they are referencing what you think
they're referencing.

            regards, tom lane