From SELECT to UPDATE in MySQL - mysql

Question

I would like you to help me with this, I have a little problem with this, but I don't know how I can fix it, basically I want to update the so called duplicatedusernameid, and update it into the users database. Here is my code:
UPDATE users SET duplicatedusernameid = (SELECT CONCAT(first_name,middle_name,last_name)
,COUNT(*)-1 AS duplicatedusernameid HAVING COUNT(*) > 1) WHERE id = 1
And here is the working SELECT function, but instead of select I want UPDATE, like the one above, but that one doesn't work. Here is the SELECT code:
SELECT CONCAT(first_name,middle_name,last_name),COUNT(*)-1 AS duplicatedusernameid
FROM users HAVING COUNT(*) > 1
So basically I want to get the value of the duplicatedusernameid and update it.

Answer 1

You can use a SQL statement like this:
update users a
inner join (
-- get the count for a user
SELECT first_name, middle_name, last_name, COUNT(*)-1 AS duplicatedusernameid
from users
group by first_name, middle_name, last_name
) b
on a.first_name = b.first_name
and a.middle_name = b.middle_name
and a.last_name = b.last_name
set a.duplicatedusernameid = b.duplicatedusernameid
where a.id = 1;
Table
create table users (
id int,
first_name varchar(100),
middle_name varchar(100),
last_name varchar(100),
duplicatedusernameid varchar(100)
);
insert into users (id, first_name, middle_name, last_name) values
(1, 'John', '', 'Smith'),
(2, 'John', '', 'Smith'),
(3, 'Jessie', '', 'Marcus'),
(4, 'Jessie', '', 'Marcus'),
(5, 'Jessie', '', 'Marcus'),
(6, 'Don', '', 'Kassieth');
Results (if you remove the where clause)
| id | first_name | middle_name | last_name | duplicatedusernameid |
|----|------------|-------------|-----------|----------------------|
| 1 | John | | Smith | 1 |
| 2 | John | | Smith | 1 |
| 3 | Jessie | | Marcus | 2 |
| 4 | Jessie | | Marcus | 2 |
| 5 | Jessie | | Marcus | 2 |
| 6 | Don | | Kassieth | 0 |
Explanation
SELECT first_name, middle_name, last_name, COUNT(*)-1 AS duplicatedusernameid
from users
group by first_name, middle_name, last_name
The above SQL statement will get the count for each unique first, middle and last name combination. You can shortlist this by adding having count(*) > 1 below the group by clause.
We then join users table with this count-related table based on first, middle and last name combination. Wherever there is a match, update the retrieved count in the users table.
SQLFiddle
http://sqlfiddle.com/#!9/c43ea/1