How to make a column unique after creating a db table?

Question

MySQL

I created a table in the database and realized that I forgot to make the column unique. I go to the "Structure" tab, check the column in A_I, save - an error pops up:

Answer 1

“Structure” tab → click next to the desired column “Primary” → “Edit” → tick A_I

Answer 2

mysql alter table
ps looked at the screenshot - and there kod_parent . I don't know how to help here.

Answer 3

A_I is not a unique column, but an auto-increment column.
Read about indexes, or rather unique indexes.

Answer 4

click the structure, look for the line where kod_parent is written in bold and on the right side of this line the squares are different, when you hover over, you can find a unique square.