Sql 如何修复ORA-01427：单行子查询返回多行？

在“客户”表中有5个客户，在“客户”表中有48个职位。“客户”表中的每个客户在“客户”表中都有8个相关职位。我想知道有多少客户在“客户服务”中拥有8个或8个以上的相关职位。如何使用select执行此操作

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提前谢谢。

您可以使用

MAX

例如：

CREATE TABLE customer ( id_customer NUMBER PRIMARY KEY, name VARCHAR2(10), surname VARCHAR2(20));

CREATE TABLE customer_wer ( id_customer NUMBER, name VARCHAR2(10), surname VARCHAR2(20), data_from DATE, data_to DATE NOT NULL, CONSTRAINT customer_wer_pk PRIMARY KEY (id_customer, data_from), CONSTRAINT customer_wer_fk FOREIGN KEY (id_customer) REFERENCES customer (id_customer));

 SELECT COUNT(customer.id_customer) 
   FROM customer JOIN customer_wer
     ON customer.id_customer = customer_wer.id_customer
  WHERE (SELECT customer_wer.id_customer 
           FROM customer_wer JOIN customer
             ON customer_wer.id_customer = customer.id_customer
          GROUP BY customer.id_customer) >= 8;

或者——如果可能的话更好——向子选择添加一些条件，以便它返回唯一的结果

如果要检查子查询返回的行之一是否为8，另一个选项是使用

IN

运算符：

SELECT COUNT(customer.id_customer) 
  FROM customer JOIN customer_wer
    ON customer.id_customer = customer_wer.id_customer
 WHERE (SELECT MAX (customer_wer.id_customer) 
          FROM customer_wer JOIN customer
            ON customer_wer.id_customer = customer.id_customer
         GROUP BY customer.id_customer) >= 8;

或者使用

EXISTS

将条件

>=8

移动到子查询中：

SELECT COUNT(customer.id_customer) 
  FROM customer JOIN customer_wer
    ON customer.id_customer = customer_wer.id_customer
 WHERE 8 IN (SELECT customer_wer.id_customer
               FROM customer_wer JOIN customer
                 ON customer_wer.id_customer = customer.id_customer
              GROUP BY customer.id_customer);

p.s.：（根据最新评论添加）

选择计数（c1.id\U客户）
来自客户c1
WHERE 2您希望查询做什么？我有两个表。一个只包含客户，第二个包含客户订单。我想知道有多少客户下了超过8个订单。添加“MAX”不起作用“独特”也不起作用。子查询必须返回几个位置。问题是我如何将几个职位与数字“8”进行比较？例如，客户有一些订单，每个客户可以有很少的订单，我如何才能只选择有8个订单的客户？操作员在

中的

是否正常工作？听起来可能。。。。如果没有：为什么？如果您需要
=8
，
存在
应该是精细的两种解决方案的结果都是0，结果应该是6。您的意思是整个
选择
？您可以先检查子查询（使用最后一条语句）。如果它不返回任何结果，则可能没有
customer\u-wer.id\u-customer>=8的行。
customer\u-wer.id\u-customer>=8的子查询不返回任何行。我的子查询“从klient\u wer中选择计数（klient\u wer.id\u klienta）在klient\u wer.id\u klienta上加入klient=klient.id\u klienta组，按klient.id\u klienta”生成6行，值为8。我需要将这6行与主查询中的数字“8”进行比较，结果应该是“6”。
SELECT COUNT(customer.id_customer) 
  FROM customer JOIN customer_wer
    ON customer.id_customer = customer_wer.id_customer
 WHERE EXISTS (SELECT customer_wer.id_customer
                 FROM customer_wer JOIN customer
                   ON customer_wer.id_customer = customer.id_customer
                WHERE customer_wer.id_customer >= 8
                GROUP BY customer.id_customer);

SELECT COUNT(c1.id_customer) 
  FROM customer c1
 WHERE 2 <= (SELECT COUNT (cw1.id_customer)
               FROM customer_wer cw1
              WHERE c1.id_customer = cw1.id_customer);