Update duplicate rows - mysql

Question

I have a table:
id name
1 a
2 a
3 a
4 b
5 b
6 c
I am looking for an update statement that will update name column to:
id name
1 a
2 a-2
3 a-3
4 b
5 b-2
6 c
In SQL Server I would use:
;with cte as(select *, row_number() over(partition by name order by id) rn from table)
update cte set name = name + '-' + cast(rn as varchar(10))
where rn <> 1
I am not strong in MySQL nonstandard queries.
Can I do something like this in MySQL?

Answer 1

You can do this:
UPDATE YourTable p
JOIN(SELECT t.id,t.name,count(*) as rnk
FROM YourTable t
INNER JOIN YourTable s on(t.name = s.name and t.id <= s.id)
GROUP BY t.id,t.name) f
ON(p.id = f.id)
SET p.name = concat(p.name,'-',f.rnk)
WHERE rnk > 1
This will basically use join and count to get the same as ROW_NUMBER() , and update only those who have more then 1 result(meaning the second,third ETC excluding the first)

Answer 2

In MySQL you can use variables in order to simulate ROW_NUMBER window function:
SELECT id, CONCAT(name, IF(rn = 1, '', CONCAT('-', rn))) AS name
FROM (
SELECT id, name,
#rn := IF(name = #n, #rn + 1,
IF(#n := name, 1, 1)) AS rn
FROM mytable
CROSS JOIN (SELECT #rn := 0, #n := '') AS vars
ORDER BY name, id) AS t
To UPDATE you can use:
UPDATE mytable AS t1
SET name = (
SELECT CONCAT(name, IF(rn = 1, '', CONCAT('-', rn))) AS name
FROM (
SELECT id, name,
#rn := IF(name = #n, #rn + 1,
IF(#n := name, 1, 1)) AS rn
FROM mytable
CROSS JOIN (SELECT #rn := 0, #n := '') AS vars
ORDER BY name, id) AS t2
WHERE t1.id = t2.id)
Demo here
You can also use UPDATE with JOIN syntax:
UPDATE mytable AS t1
JOIN (
SELECT id, rn, CONCAT(name, IF(rn = 1, '', CONCAT('-', rn))) AS name
FROM (
SELECT id, name,
#rn := IF(name = #n, #rn + 1,
IF(#n := name, 1, 1)) AS rn
FROM mytable
CROSS JOIN (SELECT #rn := 0, #n := '') AS vars
ORDER BY name, id) AS x
) AS t2 ON t2.rn <> 1 AND t1.id = t2.id
SET t1.name = t2.name;
The latter is probably faster than the former because it performs less UPDATE operations.

Answer 3

The next query will do it with less effort for the database:
UPDATE
tab AS tu
INNER JOIN
-- result set containing only duplicate rows that must to be updated
(
SELECT
t.id,
COUNT(*) AS cnt
FROM
tab AS t
-- join the same table by smaller id and equal value. That way you will exclude rows that are not duplicated
INNER JOIN
tab AS tp
ON
tp.name = t.name
AND
tp.id < t.id
GROUP BY
t.id
) AS tc
ON
tu.id = tc.id
SET
tu.name = CONCAT(tu.name, '-', tc.cnt + 1)