关于连接或子查询的sql oracle问题

Question

select *
from amazon_shipment, customer
where amazon_shipment.customer_id = customer.customer_id 
and amazon_shipment.customer_id in 
    (select top(1) amazon_shipment.customer_id
    from amazon_shipment 
    group by amazon_shipment.customer_id
    order by count(*) desc);

我试图选择订单最多的所有客户，但是，我收到一个错误：

找不到FROM关键字

Answer 1

TOP（1）在Oracle中不可用。

在Oracle 11gR2及更低版本中，您可以使用WHERE ROWNUM <2

select *
  from EMPLOYEES
 where rownum < 2
 order by SALARY desc;

在Oracle 12c及更高版本中，您只能使用FETCH FIRST 1 ROWS

select *
  from EMPLOYEES
 order by SALARY desc
 fetch first 1 rows only;