Target table cannot be same one for update clause in mysql - mysql

Question

I have a table name named 'employee'. Table creation code given below:
create table employee(name varchar(50),ph_no varchar(10),e_id varchar(5),pay_scale varchar(5),year varchar(4));
The table content is like below:
insert into employee(name,ph_no,pay_scale,year) values('AMIT','123456','PL-10','2019');
insert into employee(name,ph_no,pay_scale,year) values('AMIT','123456','PL-10','2020');
insert into employee(name,ph_no,pay_scale,year) values('AMIT','123456','PL-11','2021');
insert into employee(name,ph_no,pay_scale,year) values('AMIT','123456','PL-11','2022');
+------+--------+------+-----------+------+
| name | ph_no | e_id | pay_scale | year |
+------+--------+------+-----------+------+
| AMIT | 123456 | NULL | PL-10 | 2019 |
| AMIT | 123456 | NULL | PL-10 | 2020 |
| AMIT | 123456 | NULL | PL-11 | 2021 |
| AMIT | 123456 | NULL | PL-11 | 2022 |
+------+--------+------+-----------+------+
Now I want to update 'e_id', first it will check whether the same e_id is in the table anywhere or not, if it is not in the table then only it will update the rows with given e_id, else it will not going to update.
So, my upgradation query is below:
update employee
set e_id='0132'
where concat_ws(',',name,ph_no,pay_scale)=concat_ws(',','AMIT','123456','PL-10')
and not exists (select e_id
from employee
group by e_id
having count(*)>=1);
But it is giving the following error:
ERROR 1093 (HY000): You can't specify target table 'employee' for update in FROM clause
I have tried the below query:
update employee set e_id='0132' where
concat_ws(',',name,ph_no,pay_scale)=concat_ws(',','AMIT','123456','PL-10') and
e_id not in
(select e_id from
(select e_id from employee group by e_id having count(*)>=1) as t);
But this also cannot update the table and showing below result:
Query OK, 0 rows affected (0.01 sec)
Rows matched: 0 Changed: 0 Warnings: 0
also tried the below code:
update employee set
employee.e_id='0132' where
employee.e_id not in (select * from
(select f.e_id from
employee f inner join employee b on
b.name=f.name and b.ph_no=f.ph_no and b.pay_scale=f.pay_scale) as tmp)
and employee.name='AMIT' and employee.ph_no='123456' and employee.pay_scale='PL-10';
but this also cannot update the table and gives below result:
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
Please help. Thank you in advance.

Answer 1

NULL doesn't play the way some people expect with NOT IN: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=24c176ff4d4e2c52309aaca14cc121c5 So, just put WHERE e_id IS NOT NULL in the sub-query. Also, HAVING COUNT(*) >= 1 can be removed as it's always going to return a value of 1 or more...
update
employee
set
e_id='0132'
where
name = 'AMIT'
and ph_no = '123456'
and pay_scale = 'PL-10'
and e_id not in (select e_id from
(select distinct e_id
from employee
where e_id IS NOT NULL
)
as t
);
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=2a0b036a7d1db9138e3ab29af3d346f8