The first step is ok,the stage becomes "submitted" by the button ,
the button have set-workflow-stage() action, then I save/submit the form
data，then I enter the summary page, but when I open the form data again,
the stage is null.
I'm sure the stage becomes "submitted" because I added a control in
the form to display the value of the stage by fr:workflow-stage-value()
function,when I click the button the control value becomes "submitted",when
I open it again, the control value is null.
This is my problem.
You are correct, for the stage feature to work, you need to be using a
relational database. I updated the release notes to make that clearer. At
some point, we should also switch to using an embedded relational database,
as most new features are only developed for relational databases.
For the DDL, you need to use `postgresql-2019_1.sql`, as that DDL hasn't
changed since version 2019.1.