When we create extension that holds tables, the MSSQL uniqueidentifier field type, is proposed to be 'text' in integration studio.
If you use it as text, then using 'advanced sql' widget, its not straightforward to compare tables value with lets say '' empty string. Because now outsystems suppose it is text, and comparison field = '' doesnt cause any errors within 'service studio'.
However, when OutSystems executes the query at the database, we get error that '' 'cannot be converted to uniqueidentifier'.