How to prevent duplicate entry key when update - mysql

Question

Problem explain
I won't update the last primary key of the 3 primary key concatenate. But the problem is sometimes the first and second primary key was the same for multiple records. And in this case, when I set my new value I have a duplicate entry key even I use sub-request to avoid that problem.
Some Code
Schemas
create table llx_element_contact
(
rowid int auto_increment
primary key,
datecreate datetime null,
statut smallint default 5 null,
element_id int not null,
fk_c_type_contact int not null,
fk_socpeople int not null,
constraint idx_element_contact_idx1
unique (element_id, fk_c_type_contact, fk_socpeople)
)
Update request
this request return duplicate key error
update llx_element_contact lec
set lec.fk_socpeople = 64
where
-- Try to avoid the error by non including the values that are the same
(select count(*)
from llx_element_contact ec
where ec.fk_socpeople = 64
and ec.element_id = lec.element_id
and ec.fk_c_type_contact = lec.fk_c_type_contact) = 0
Test data
rowid, datecreate, statut, element_id, fk_c_type_contact, fk_sockpeople
65,2015-08-31 18:59:18,4,65,160,30
66,2015-08-31 18:59:18,4,66,159,12
67,2015-08-31 18:59:18,4,67,160,12
15283,2016-03-23 11:47:15,4,6404,160,39
15284,2016-03-23 11:51:30,4,6404,160,58

Answer 1

You should check only two other members of unique constraint as you're trying to assign the same value to the 3d member. No more then one row with the same two members must exist.
update llx_element_contact lec
set lec.fk_socpeople = 64
where
-- Try to avoid the error by non including the values that are the same
(select count(*)
from llx_element_contact ec
where ec.element_id = lec.element_id
and ec.fk_c_type_contact = lec.fk_c_type_contact) <=1
or
update llx_element_contact lec
set lec.fk_socpeople = 64
where
-- Try to avoid the error by non including the values that are the same
not exists (select 1
from llx_element_contact ec
where ec.element_id = lec.element_id
and ec.fk_c_type_contact = lec.fk_c_type_contact
and lec.fk_socpeople != ec.fk_socpeople)

Answer 2

You can use:
You can prevent the unique conflict using left join to check that the corresponding row doesn't already exist:
update llx_element_contact lec left join
(select element_id, fk_c_type_contact
from llx_element_contact lec2
where lec2.fk_socpeople = 64
group by element_id, fk_c_type_contact
) lec2
using (element_id, fk_c_type_contact)
set lec.fk_socpeople = 64
where lec2.element_id is null;
Your query has additional logic in it that is not explained. It is not necessary for what you are asking.

Answer 3

WITH cte AS (
SELECT rowid,
SUM(fk_socpeople = 64) OVER (PARTITION BY element_id, fk_c_type_contact) u_flag,
ROW_NUMBER() OVER (PARTITION BY element_id, fk_c_type_contact ORDER BY datecreate DESC) u_rn
FROM llx_element_contact
)
update llx_element_contact lec
JOIN cte USING (rowid)
set lec.fk_socpeople = 64
where cte.u_flag = 0
AND cte.u_rn = 1
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=08e20328ccc6187716084ce9d78816b0