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From Deepak Kapoor <dkapoor...@gmail.com>
Subject Would you expect coalesce to return a result when none of the columns in coalesce exist in the parquet file ??
Date Thu, 23 Aug 2018 23:18:21 GMT
Would you expect coalesce to return a result when none of the columns in coalesce exist in
the parquet file ??

Query 1:
select coalesce(cert_statusdd,cert_status33) from dfs.`/tmp/parquetfiles`;
Error: SYSTEM ERROR: CompileException: Line 56, Column 27: Assignment conversion not possible
from type “org.apache.drill.exec.expr.holders.NullableIntHolder” to type “org.apache.drill.exec.vector.UntypedNullHolder”

Fragment 1:0

[Error Id: 7b9193fb-289b-4fbf-a52a-2b93b01f0cd0 on dkvm2c:31010] (state=,code=0)

In above case both the columns do not exist.  Is the error reported a valid error or is it
a bug.

Another observation is that if you use CAST on the column that does not exist, Coalesce will
not error out instead return nulls. 
Query 2:
select coalesce(cast(cert_statusdd as varchar),cast(cert_statusee as varchar)) from dfs.`/tmp/parquetfiles`
limit 3;
+---------+
| EXPR$0  |
+---------+
| null    |
| null    |
| null    |
+————+

Note: Databases like postgresql and mysql will not allow COALESCE on non existing column,
w or without CAST. 
Drill however being schema free, do we expect COALESCE to succeed and give null as result
?? In which case the SYSTEM ERROR: CompileException with the 1st Quert  be a bug. ??

Thanks.
- Deepak (dkapoor@mapr.com <mailto:dkapoor@mapr.com>)


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