你可以在下面试试

select id,a.customerid, case when cnt=1 then 1 else 0 end as Unique_Flag
from tablename a 
left join 
(select customerid, count(*) as cnt from tablename
group by customerid
)b on a.customerid=b.customerid

您似乎想将第一个事件标记为唯一的，而不是其他事件。那么，让我们加入比较值：

select t.*,
       (id = min_id) as is_first_occurrence
from t join
     (select customer_id, min(id) as min_id
      from t
      group by customer_id
     ) tt
     on t.customer_id = tt.customer_id;

对大多数人来说，“唯一”标志意味着总计数是“1”，而不是仅仅是第一次出现。如果这就是你想要的，那么你可以使用类似的逻辑：

select t.*,
       (id = min_id) as is_first_occurrence,
       (cnt = 1) as is_unique
from t join
     (select customer_id, min(id) as min_id, count(*) as cnt
      from t
      group by customer_id
     ) tt
     on t.customer_id = tt.customer_id;

在mysql 8+中，您将使用窗口函数：

select t.*,
       (row_number() over (partition by customer_id order by id) = 1) as is_first_occurrence,
       (count(*) over (partition by customer_id) = 1) as is_unique
from t;

您可以使用下面给出的lead函数来获得所需的输出。 SELECT ID, CUSTOMER_ID, CASE WHEN CUSTOMER_ID != CUSTOMER_ID_NEXT THEN 1 ELSE 0 END AS UNIQUE_FLAG FROM (SELECT ID, CUSTOMER_ID,LEAD(CUSTOMER_ID, 1, 0) OVER (ORDER BY CUSTOMER_ID) AS CUSTOMER_ID_NEXT FROM TABLE)T