Add a specific field into table in SQL

Question

I a table like this:

date time user data
131111 111111 Mike 23
131111 121212 Linda 12
131111 131323 Mike 45

I want to add a field called "userID", based on the existing data in the DB:

date time user userID data
131111 111111 Mike 1 23
131111 121212 Linda 2 12
131111 131323 Mike 1 45

As long as the userID is one-on-one mapping to an existing user, it would be fine. It would be better if it starts from 1 to #ofUsers.

Is there a clean solution?

Answer 1

Try something like this:

First you add the new column:

ALTER TABLE tab1 ADD userid INT NOT NULL;

Then you do:

UPDATE tab1 t1
INNER JOIN (  
SELECT a.user, @rownum := @rownum + 1 AS newID
  FROM (
    SELECT DISTINCT user
    FROM tab1
    ORDER BY user
    ) a
  JOIN (
    SELECT @rownum := 0
    ) r
) t2 ON t1.user = t2.user
SET t1.userid = t2.newID

sqlfiddle demo

The inner query, gets a unique id to each distinct user (starting at 1 and increasing alphabetically. You can remove the order by if you don't care about any order) in the table and updates your table accordingly.

Hope this helps.

Answer 2

ALTER TABLE mytable ADD userID INT;

UPDATE mytable, usertable 
SET mytable.userID = usertable.ID 
WHERE usertable.user=mytable.user;