Oracle: column ambiguously defined

Question

I know there are lots of questions like these, but my question is not how to get rid of this error but to know how this worked earlier in 9-th version of Oracle.

I've got an old sources written in Ruby and Oracle DB which recently was upgraded to version=11.

I cannot edit data in Oracle DB, only read. so there are two tables lets say: table A(id, name, type, customer) and table B(id,a_id,type,person)

so. there is a query in the source code:

select a.id,b.id from a join b on a.id = b.a_id where type = 'A'

so in Oracle 9 this worked perfectly but now i've got "column ambiguously defined" error.

What i'd like to know is:

where type = 'A'

is the same as

where a.type = 'A' AND b.type = 'A'

or

where a.type = 'A' OR b.type = 'A'

?

Answer 1

I think this was a bug with the ANSI style join. Use DBMS_XPLAN to find which table was being filtered in the old database.

Or better still, work out from the business logic what they query SHOULD have been.

Answer 2

No, and that's the problem: It could mean

where a.type = 'A'

or it could mean

where b.type = 'A'

with potentially different results; hence the error saying it is ambiguously defined.

Answer 3

I think you should test in Oracle 9 (where you say it works) and compare the output of the ambiguous query:

--- Base
select a.id,b.id from a join b on a.id = b.a_id where type = 'A'

with both the non-ambiguous ones:

--- QueryA
select a.id,b.id from a join b on a.id = b.a_id where a.type = 'A'

and:

--- QueryB
select a.id,b.id from a join b on a.id = b.a_id where b.type = 'A'

---

Something like this would do:

select a.id,b.id from a join b on a.id = b.a_id where type = 'A'
MINUS
select a.id,b.id from a join b on a.id = b.a_id where a.type = 'A'

(in short):

(Base)
MINUS
(QueryA)

and then:

(QueryA)
MINUS
(Base)

If both of the above MINUS queries return 0 rows, then BASE query is interpreted as QueryA.

Check similarly and compare Base with QueryB.

---

Another plausible reason for this error is that during (or about the same period with ) the migration, a type column was added in the 2nd table. Do you have old versions of the database tables' definitions to check that?

Answer 4

All - keep in mind there was a major change to the optimization engine for 11g. If you set your query optimizer level to 10.2.x on your 11g instance I bet the query would start working again.

That being said you should provide the alias for it so it's not ambiguous to the database server or the DBA / Developer coming behind you. :)