MySQL: fix fully duplicate row - php

Question

I have table tags and I forget to set id column as primary key when created it.
Now I am facing a duplicate key problem.
tags table:
id text
1 man
2 ball
2 ball
2 ball
3 love
3 love
4 heart
4 heart
How to remove duplication and keep and set id as the primary key ?
Expected result: ( the new required tags table)
id text
1 man
2 ball
3 love
4 heart

Answer 1

I think the easiest way is to create a temporary table with the data and then reload the data:
create temporary table tags_temp as
select distinct id, text
from tags;
truncate table tags;
alter table tags add primary key (id);
insert into tags(id, text)
select id, temp
from tags_temp;

Answer 2

What I would do, is create a new table, add the key insert the data from the old table, then drop tags and rename temp
/* Make a copy of the database table (including indexes) */
create table tags_tmp like tags;
/* Add the primary key to the table */
alter table tags_tmp add primary key (id);
/* Insert the data from the bad table and ignore any duplicates */
insert ignore into tags_tmp (id, text)
select id, text from tags;
/* Drop the bad table */
drop table tags;
/* Rename the temporary table to the original name */
rename table tags_tmp to tags;

Answer 3

First, I created your table and inserted data in:
mysql> select * from tags;
+----+-------+
| id | text |
+----+-------+
| 1 | man |
| 2 | ball |
| 2 | ball |
| 2 | ball |
| 3 | love |
| 3 | love |
| 4 | heart |
| 4 | heart |
+----+-------+
8 rows in set (0.00 sec)
I backup the distinct entries only:
mysql> create table T as select distinct * from tags;
Query OK, 4 rows affected (0.27 sec)
Records: 4 Duplicates: 0 Warnings: 0
I no longer need the original table, so I drop it from the database:
mysql> drop table tags;
Query OK, 0 rows affected (0.12 sec)
I rename the previous backup table:
mysql> rename table T to tags;
Query OK, 0 rows affected (0.08 sec)
Now it is time to add the PRIMARY KEY constraint to our table:
mysql> alter table tags add primary key(id);
Query OK, 0 rows affected (0.48 sec)
Records: 0 Duplicates: 0 Warnings: 0
Now, let us test if what we did is correct. First, let us display the data:
mysql> select * from tags;
+----+-------+
| id | text |
+----+-------+
| 1 | man |
| 2 | ball |
| 3 | love |
| 4 | heart |
+----+-------+
4 rows in set (0.00 sec)
Let's try to add a row with id = 4:
mysql> insert into tags values(4,'proof');
ERROR 1062 (23000): Duplicate entry '4' for key 'PRIMARY'
Conclusion: what we did is correct.