Hello menayah,
so when you write to the on premise DB you do not have any performance problems but only when writing to the Azure SQL instance? Did you create all indices especially the one for the lookup column in the Azure SQL table?
I guess you mean the Microsoft SQL Server Connector node with the Knime Server Connector node. What mapping did you use for String columns or this particular column? The default mapping for String columns in the Microsoft SQL Server Connector node is VARCHAR
In this case KNIME uses the PreparedStatement.setString() method to send the string values to the database. However if the mapping for String columns is set to NVARCHAR the PerparedStatement.setNString() method is used instead.
Maybe this is also a driver related issue. Can you please updated the JDBC driver to the latest version. For more details on how to register a driver see this documentation.
Bye
Tobias