Hello, I am trying to write an INSERT query for DB2 using the Query D

Rather than doing this directly in the SQL statement, you could do it beforehand in a script task. Set up a script task node prior to the query database node. Then have the script task run some if() statement logic to determine whether ac!VarcharField should be null or have an actual value

How can i define the ac!VarcharField (DataType Text) to have a null value?

null is reserved in Appian, so you can just set up a data input or output and assign 'null' (without the quote marks) to ac!VarcharField

Thank you for your help. However, even with assigning 'null' to the parameter ac!VarcharField, the respective DB field contains an empty string value ('') and not a NULL value.

Are you sure that the value of ac!VarcharField isn't being overwritten anywhere else after it is given null?

Yes, i am sure that the value of ac!VarcharField is not being overwritten by another value. I have also tried this functionality on a new test process model that only executes the same INSERT query and it ONLY provides the value 'null' to ac!VarcharField. The resulting value in the DB field is always the same.

Is the field in the database configured as "NOT NULL"?

No, the field is configured to allow NULL values.

We're using MS SQLServer, but we also have the issue that whenever using write to datastore entity and passing in nulls, Appian passes empty strings to varchar fields "". We have an enhancement request for this issue with reference number AN-53545. We've had to work around this by either accepting "" in the database, creating smaller CDTs that don't include the fields that are being left null (only works if we know those fields wouldn't be populated in that process), having triggers on the database that will set the fields to null, or using the Execute stored procedure plugin and creating stored procedures for our data writes.