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I would like to update multiple rows in one single query by using UPDATE CASE scenario in mySQL. I am building my web app using python and Django. Here is my code:

UPDATE order
SET priority_number =
    CASE priority_number
    WHEN 2 THEN 3  
    WHEN 3 THEN 4
    WHEN 1 THEN 5
    WHEN 4 THEN 2
    WHEN 5 THEN 1
END

So this single query will update all field as I desire. My question is, how can I program this if I have an unknown number of rows to update? Lets say all these numbers comes from an array that I will pass into my views and I don’t know how many WHEN and THEN statement I need to write? thanks for your help!

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1 Answer 1

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You can programmatically build up a query, using the conditionals Case and When.

So, for example:

from django.db.models import Case, When

# Make a list of When expressions
when_list = [When(priority_number=2, then=3),
             When(priority_number=3, then=4)]

# Use in a query of your choice, as an example:
Model.objects.update(
    priority_number=Case(
        *when_list))
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5 Comments

Hello, thanks for the respond! where can I pass my array here?
OP search the solution for update not for select
Updated the answer to include a list.
Hi, I created a lists of WHEN as you mentioned. But when I pass it as *when_list into the Case (per your example) it is literally trying to execute *when_list and not whats in that lists. Any advise?
Sorry, I forgot to import. Let me try again!

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