Question

I want to calculate the addition with exisiting value.

e.g. MySQL:

   UPDATE TBL SET val = +1 WHERE id = 1

How can I do in SQLAlchemy?

Thanks.

Answer 1

You can do this via the SQLAlchemy Core via just referencing the field name (example taken from here):

>>> conn.execute(users.update().
...                     values(fullname="Fullname: " + users.c.name)
...                 )

In your case, this would probably look something like…

conn.execute(your_table.update().values(val=your_table.c.val + 1))

If you need more complex behavior, you can look at correlated updates: essentially, creating a select object that represents the new value you want (based on the old one) and setting that as the value in your update object’s values.