create table it1120 (
  id int unsigned not null auto_increment primary key
, name text
, idate date
);

insert into it1120 (name,idate) values
 ('小島南',  '2021-11-01')
,('小島南',  '2021-11-01')
,('小島南',  '2021-11-03')
,('小島南',  '2021-11-03')
,('初川南',  '2021-11-01')
,('初川南',  '2021-11-01')
,('初川南',  '2021-11-02')
,('相澤南',  '2021-11-01');


select name
  from it1120
 group by name
having count(name) > 1;

+-----------+
| name      |
+-----------+
| 小島南    |
| 初川南    |
+-----------+
2 rows in set (0.01 sec)

select id, name, idate
     , row_number() over(partition by name order by idate) as rn1
  from it1120
 order by id;
 
+----+-----------+------------+-----+
| id | name      | idate      | rn1 |
+----+-----------+------------+-----+
|  1 | 小島南    | 2021-11-01 |   1 |
|  2 | 小島南    | 2021-11-01 |   2 |
|  3 | 小島南    | 2021-11-03 |   3 |
|  4 | 小島南    | 2021-11-03 |   4 |
|  5 | 初川南    | 2021-11-01 |   1 |
|  6 | 初川南    | 2021-11-01 |   2 |
|  7 | 初川南    | 2021-11-02 |   3 |
|  8 | 相澤南    | 2021-11-01 |   1 |
+----+-----------+------------+-----+
8 rows in set (0.00 sec)

with t1(id, rn) as (
select id
     , row_number() over(partition by name order by idate) as rn1
  from it1120
)
delete
  from it1120
 where id in (
       select id 
          from t1
         where rn > 1);

Query OK, 5 rows affected (0.01 sec)

select * from it1120;
+----+-----------+------------+
| id | name      | idate      |
+----+-----------+------------+
|  1 | 小島南    | 2021-11-01 |
|  5 | 初川南    | 2021-11-01 |
|  8 | 相澤南    | 2021-11-01 |
+----+-----------+------------+
3 rows in set (0.00 sec)

作為刪除的條件式，你的子查詢中回傳的唯一欄位 MIN(last) 會是一個數值，而不是你要用來當作刪除條件的 name

這個我大概知道你想要做甚麼@@..
你想要把重複資料變成1筆對吧~
若是這樣~我的作法是將資料group後~複製到暫存的新表~
清空原表資料~再從暫存新表新增回來~

答案我不會
題目是「如何將相同資料刪掉只剩一筆」
刪成像最下面那個 select 的結果一樣

db fiddle

假設如同純真的人說的【要把COUNT(name) > 1的多餘資料刪除】，在借用海綿寶寶建的資料，SQL 如下:
tname = Blue,tlast = 10 要另外處裡

create table data
(tname varchar(20),
tlast int);

insert into data values ('Alex', 50);
insert into data values ('Blue', 10),('Blue', 10);
insert into data values  ('Eva', 201), ('Eva', 301), ('Eva', 401);
insert into data values ('rex0220', 100), ('rex0220', 200), ('rex0220', 200);

DELETE FROM data
WHERE tlast NOT IN (
SELECT * FROM (
SELECT MIN(tlast) FROM data 
GROUP BY tname
) AS A)

Demo