用这个。

SELECT tbl.id
      ,tbl.cust_id
      ,tbl.cust_name
      ,(SELECT COUNT(cust_id)
        FROM Mytable
        WHERE cust_id = tbl.cust_id) AS status
FROM MyTable tbl;
-- to update table
-- first create a dummy table
create table tbl as select tbl.id, tbl.cust_id, tbl.cust_name, (select count(cust_id) from Mytable where cust_id = tbl.cust_id) as status from MyTable tbl;
-- drop original
drop table mytable;
-- rename dummy
alter table tbl rename to mytable;

WITH CTE
(
select custid,count(1) cnt
from my_table
group by custid
)
UPDATE a SET a.status= CASE WHEN b.cnt = 1 THEN 1 ELSE 2 END
FROM my_table a
INNER JOIN CTE b
on a.custid=b.custid

试试这个：

declare @tbl table (ID int,  CustId char(2), CustName char(1), Status int);
insert into @tbl values
(1,'a1','A',NULL),
(2,'a1','A',NULL),
(3,'a2','B',NULL),
(4,'a3','B',NULL),
(5,'a4','C',NULL),
(6,'a4','C',NULL),
(7,'a5','D',NULL),
(8,'a6','E',NULL);

update t1 set t1.Status = case when t2.st > 1 then 2 else 1 end
from @tbl t1
join (select ID, COUNT(*) over (partition by custname) st from @tbl) t2
on t1.ID = t2.ID

select * from @tbl

使用联接更新：
它将在sql server中工作：

update tablename set status=cstatus
from tablename inner join
(
select custid, count(custid) as cstatus
from tablename)b on tablename.custid=b.custid

在mysql中，以下命令将起作用

UPDATE tablename
    JOIN (
    select custid, count(custid) as cstatus
    from tablename)b on tablename.custid=b.custid
SET set status=cstatus