MYSQL: Create Unique ID based on Another Column - mysql

Question

If I have the following column in database:
Email
aaa#gmail.com
ccc#gmail.com
ddd#gmail.com
ccc#gmail.com
bbb#gmail.com
aaa#gmail.com
I would like to ALTER THE TABLE and create a unique ID column based on the 'Email' column. Like the following:
Email Email_ID
aaa#gmail.com 001
ccc#gmail.com 002
ddd#gmail.com 003
ccc#gmail.com 002
bbb#gmail.com 004
aaa#gmail.com 001

Answer 1

I would suggest that you use an integer for the value -- rather than a string. Then, you can use variables as for the assignment:
alter table t add email_id int;
update t join
(select email, (#rn := #rn + 1) as rn
from (select distinct email from t order by email) t cross join
(select #rn := 0) params
) tt
on t.email = tt.email
set t.email_id = tt.rn;
If you run the subquery, you will see that this assigns to each email a distinct number.
The outer query then assigned this number into the email_id column. In MySQL 8+, you could also write:
alter table t add email_id int;
update t join
(select email, row_number() over (order by email) as rn
from (select distinct email from t order by email) t
) tt
on t.email = tt.email
set t.email_id = tt.rn;

Answer 2

If you are using MySQL version 8 or later, then DENSE_RANK provides a nice option here:
SELECT
Email,
LPAD(CAST(DENSE_RANK() OVER (ORDER BY Email) AS CHAR(3)), 3, '0') AS Email_ID
FROM yourTable
ORDER BY
Email;
I would have suggested maybe just adding an auto increment column to your table, but that wouldn't quite meet your requirements, because an auto increment column would always be unique.

Answer 3

Here's what I'd do...
Create a new table with a unique email column
CREATE TABLE `emails` (
id INT(3) PRIMARY KEY AUTO_INCREMENT,
email VARCHAR(255) UNIQUE
);
Seed it with your current data
INSERT INTO `emails` (`email`)
SELECT DISTINCT `email` FROM `some_mystery_table`
ORDER BY `email`;
Alter your existing tables to reference emails(id) as a foreign key. This could be a little tricky as you'd need to (probably)
Add a new int column email_id where required
Update your data with the id value corresponding to the email address
UPDATE some_mystery_table, emails
INNER JOIN emails ON some_mystery_table.email = emails.email
SET some_mystery_table.email_id = emails.id;
Remove the email column
Add a foreign key where email_id references emails(id)
When displaying your data and you need a zero-padded email id, join the emails table, eg
SELECT a.whatever, e.email, LPAD(e.id, 3, '0') AS email_id
FROM some_mystery_table a
INNER JOIN emails e ON a.email_id = e.id;
When adding new email records, you add them to emails first, then use the generated id in any other related tables.

Answer 4

ALTER TABLE emails add column `email_id` int(5) ZEROFILL PRIMARY KEY AUTO_INCREMENT;
SET #x:=0;
UPDATE emails SET email_id = LPAD(#x:= (#x+1),4, '0') WHERE 1=1;
We first added the column email_id to the table emails and set it as primary key, using this query:
ALTER TABLE emails add column `email_id` int(5) ZEROFILL PRIMARY KEY AUTO_INCREMENT;
Then we declared a global variable called x with a default value of 0:
SET #x:=0;
And finally, we filled the column with the incremental zero filled id:
UPDATE emails SET email_id = LPAD(#x:= (#x+1),4, '0') WHERE 1=1;
We used LPAD to zero fill.