@sas_pkc1
There is not a simple anwser to your question so just let me throw in a few thoughts and pointers.
The root issue here is the filed length difference betwen your staging table and your target table column. It appears that this column should map 1:1 from source to target. You say that the actual strings in this columns are shorter than the length in the target column - but that's not the solution to the issue.
Your source and target columns must match OR you have a clear business rule defined of how to transform the column (=read only the first n characters from source). I believe you have neither.
If you don't have a business rule for such a transformation then you need either to discuss with your data provider (the one providing the staging table) and the Interface Contract needs change so that the source column matches the target column OR you need to talk to the owner of the target model so that the column in the target model gets changed to match the source.
If you don't do this then you risk that one day a string comes which is actually 1000 characters long and you then truncate it when loading into target. You would be the one to be blamed if you've implemented something like this without a clear business rule.
Why is it not loading?
Highly likely because you're doing something wrong. What does the SAS log tell you?
How do you test? If you're using SQL Developer or the like then don't forget to issue a commit after insert/update/delete or you won't see the changes.
If source and target are in Oracle then I normally try and keep all processing in Oracle. How easily that's possible using DIS will depend on the transformation steps.
In order to give you advice you need as a first step to share the load log with us, a screenshot of the DIS flow section where this load happens and the generated code for this sections. We can't know what you've got wrong that this is not working.
As for the SAS log: Please add options sastrace=',,,d' sastraceloc=saslog nostsuffix; before the load step (ie. as pre-code) so we get more information in the SAS log.
Please provide SAS log and DIS generated code as text file attachments and don't just copy/paste it directly into this thread.
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