I was trying to put one of my tables as primary key .
As soon as I try, the message appears:
# 1062 - Duplicate entry for key 'PRIMARY'
The data is populated and looks something like this:
I tried to put Sub_Id as the primary key.
As reported by the error message, the sub_id field is not unique and repeats.
It seems to me that your table has a key composed of area_id and sub_id . Try setting the both columns as the primary key:
ALTER TABLE tabela
ADD CONSTRAINT pk_AreaId_SubId PRIMARY KEY (area_id,sub_id);
Alternatively, you can create a new column to be the primary key ( Surrogate Key ):
ALTER TABLE tabela
ADD id_pk INT NOT NULL PRIMARY KEY AUTO_INCREMENT FIRST;
More information about ALTER TABLE in the MySQL documentation .
Do the following query and see the cause of the problem:
SELECT SUB_ID, COUNT(*) TOTAL FROM TABELA GROUP BY SUB_ID HAVING COUNT(*) > 1