Github user jihoonson commented on the pull request:
https://github.com/apache/tajo/pull/543#issuecomment-94567939
Thanks @dongjoon-hyun. The newly added test looks good, but have a
limitation. That is, it cannot test that the qualifier is properly guessed for
the simple column name in order-by clause. So, we need a test case to check the
query execution result in addition to the plan test.
In addition, I found that this patch cannot handle the case when there are
a column and an alias of same name. Please see the following example.
*Postgresql*
```
# explain select r_name as n_name from nation, region order by n_name;
QUERY PLAN
-------------------------------------------------------------------------
Sort (cost=284.00..293.25 rows=3700 width=32)
Sort Key: region.r_name
-> Nested Loop (cost=0.00..64.71 rows=3700 width=32)
-> Seq Scan on nation (cost=0.00..17.40 rows=740 width=0)
-> Materialize (cost=0.00..1.07 rows=5 width=32)
-> Seq Scan on region (cost=0.00..1.05 rows=5 width=32)
(6 rows)
```
*Tajo*
```
default> explain select r_name as n_name from nation, region order by
n_name;
ERROR: Ambiguous column name: n_name
```
I think that this case also handled in this patch.
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