MySQL deduplication and nested Deletion

The table EMP contains the primary key empid. Now I want to delete the record with duplicate non-primary key fields empno. For more information, see write a specific statement. If you copy the record from other problems, do not post it.

The Delete action of MySQL cannot contain the query action of the table, which means that the deletion of Table A cannot be based on the information of Table: delete from a where AA in (select bb from );
You can create another table and perform two table matching operations, for example, create table T_ B as select * From T_A group by empno;

Delete from T_A where empid not exists (select 1 from T_ B where t_a.empid = t_ B .empid );