Hi,

while I was writing this, I solved the issue myself, but I am submitting 
the text anyway, since there is still an open question.

My problem was:
I am getting a data convesion error without specification on the 
column/data just as follows:
"Data conversion error converting ; SQL statement: ... "
then the SQL follows.

Some background infos:
- I am running H2 with an embedded database
- I am getting the error with version 1.4.x (also the most recent)
- I am getting NO error with 1.2
- I am getting the error while querying a SELECT with LEFT JOINs - BUT: 
only, if the LEFT JOIN is empty, meaning if the joined tables do not 
contain relatable content
- the query is run from a swing application not in the AWT thread but in a 
different thread
- if I run the same query on the same database using a small test class, 
the query performs without error
- I am getting the error using either mvstore or pagestore

I downloaded the H2 source and tried to follow, where the exception is 
thrown, and it's somewhere in the Prepared.query() method. I can't pinpoint 
the exact line, because the debugger does not show the correct lines 
(although I did a clean&build).

I just pinpointed the problematic select field:
  
SELECT
 ...
 ,IFNULL(ele.number,'') || '.' || IFNULL(obs.number,'') AS fullnumber
 ...

... this line is concatenating two fields, the second (obs.number) is null, 
if the left join is empty.

I found the changelog not for 1.4.192:
  The function IFNULL did not always return the result in the right data 
type. 

The number fields are of type BIGINT ... there might be a concusion due to 
mixing bigint fields with string results if the IFNULL returns true...
It is working perfectly with the select specified as

  ,IFNULL(ele.number,0) || '.' || IFNULL(obs.number,0) AS fullnumber

But then: why does it work with the small test class?

Thanks, Hannes

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