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Adding new virtual column with instant algorithm
Posted by: Lawrence Marigold
Date: December 09, 2020 08:58AM

Hi,

I'm trying to add a generated column using the instant algorithm on an InnoDB table on MySQL 8.0.22 on Windows Server 2012.

Whatever I try however it gives me the same error:

"Error Code: 1846. ALGORITHM=INSTANT is not supported. Reason: INPLACE ADD or DROP of virtual columns cannot be combined with other ALTER TABLE actions. Try ALGORITHM=COPY/INPLACE."

The original (simplified) query is like this:

"alter table contacts add column (test boolean generated always as (if(data->>'$.test' is null or data->>'$.test' = 'false',false,true)) virtual), ALGORITHM INSTANT"

contacts.data is a json column.

I thought the issue might be to do with accessing the json, so I tried the most simple genrated column I can imagine with the exact same error:

"alter table contacts add column (test boolean generated always as (false) virtual), ALGORITHM INSTANT;"

I don't understand what other actions are being performed which are causing the error, and as I understood it, virtual columns are one of the actions that are specifically supposed to be supported by the instant algorithm.

If I exclude the algorithm part of the command it does work, but is quite slow, which is not ideal for what we are trying to achieve.

Am I missing something?

Thanks - Lawrence

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