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I already have a table with some data in it. And now I want to add a new column "id" and make it a primary key. I'm using MySQL Workbench. So, I'm just adding a new key and then setting it as PK and NN. But for some reason, this apparently simple and straightforward operation doesn't work. I get:

ERROR 1062: Duplicate entry '0' for key 'PRIMARY'

Why is that?

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You probably already have a field set as primary key in that table. I guess you would have to disable that field as PK and add the new id-column in the same statement.

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4 Comments

I don't have any other primary key.
@VisanCosmin Could you please add your SQL-Statement and column definitions of your table to your question?
I'm using mySql Workbench. I'm just selecting PK and NN and click apply. (I cannot insert a picture, because I don't have reputation at least 10.)
All I can think of is backing up the table data and recreate the table. Maybe this will help.

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