Mysql error Operand should contain 1 column(s)
1. An error
ERROR 1241 (21000): Operand should contain 1 column(s)
2. Report the cause of the error
This statement mostly occurs because the result set of the SELECT is wrapped in (). It is normal to enclose () with select, but it is possible that the fields are misused, as shown in the following SQL:

select 
 pit_key
,employee_code
,department_id
,value_date
from pit_employee_department ped
where ped.employee_code = 'GSCQ3349'
and ped.value_date < date_format(date_sub(curdate(), interval day(curdate()) - 1 day),'%Y%m%d')
and ped.pit_key not in
(	select 
	pit_key
	,value_date
	from pit_employee_department ped_1
	inner join 
	(
		select 
		max(value_date) as max_date
		from pit_employee_department ped

		where ped.value_date <= date_format(date_sub( date_sub(curdate(), interval day(curdate()) - 1 day),interval 1 month),'%Y%m%d')
		and employee_code = 'GSSH0039'
	)ped_2
	on ped_1.value_date < ped_2.max_date
	and ped_1.employee_code = 'GSSH0039'
);

The reason for executing this error in the above SQL statement is that pit_key and value_date are used in the subquery, and the comparison option is pit_key not in (...). , field inconsistency results in an error.
3. Solutions
Make changes for different reasons.