MySQL PHPMyAdmin Error #1062 - Duplicate entry 

Question

Now I want to add a primary key id column but it throws the error:

#1062 - Duplicate entry '0' for key 'PRIMARY'

I already tried this: Add primary key to existing table

Answer 1

When you creates a new column, a default value is asigned (in your case will be 0), so you need to specify wich values will it have (besides you can tell it to the column to be autoincremental, and it will do the work for you for the new entries of rows). You have to change all the values to be differents between them, the id key MUST be unique

To change all your ids, in mysql you can do:

SET @new_id=0;
UPDATE your_table
SET id = @new_id := @new_id + 1
where id = 0

Answer 2

First please change ids of the table with below query

SET @counter = 1
UPDATE #tablename
SET @counter = id = @counter + 1

And then Apply primary key.