Question

我需要列出成对的客户名称，如下所示;

> CUSTOMER_FIRST_NAME, CUSTOMER_LAST_NAME, CUSTOMER_FIRST_NAME, CUSTOMER_LAST_NAME

这样每对客户都有相同的邮政编码（也在客户表中）。

在任务上有一个提示

提示：您的输出应该有四列：CUSTOMER_FIRST_NAME，CUSTOMER_LAST_NAME，CUSTOMER_FIRST_NAME，CUSTOMER_LAST_NAME

这是我到目前为止所写的：

SELECT DISTINCT CUSTOMER_FIRST_NAME, CUSTOMER_LAST_NAME, CUSTOMER_FIRST_NAME, CUSTOMER_LAST_NAME
FROM CUSTOMERS
WHERE CUSTOMER_ZIP = CUSTOMER_ZIP

但我不确定如何继续，因为我昨天才开始学习SQL。我也尝试加入同一个表格，导致模糊错误。

更新＃1： 我按照@ kpater87

的建议使用别名编写了这段代码

 SELECT DISTINCT  C1.CUSTOMER_FIRST_NAME, C1.CUSTOMER_LAST_NAME , C2.CUSTOMER_FIRST_NAME, C2.CUSTOMER_LAST_NAME 
FROM CUSTOMERS C1
INNER JOIN CUSTOMERS C2
ON C1.CUSTOMER_ZIP = C2.CUSTOMER_ZIP

但即使我有一个明确的声明，它也会显示重复的数据。这是预期还是我错过了什么？

Answer 1

您的更新查询看起来很好。您的查询中唯一的问题是它将加入相同的记录。如果表格中有主键，则可以通过添加WHERE条件来改进查询：

SELECT DISTINCT C1.CUSTOMER_FIRST_NAME,
  C1.CUSTOMER_LAST_NAME ,
  C2.CUSTOMER_FIRST_NAME,
  C2.CUSTOMER_LAST_NAME
FROM CUSTOMERS C1
INNER JOIN CUSTOMERS C2
ON C1.CUSTOMER_ZIP = C2.CUSTOMER_ZIP
WHERE C1.PK <> C2.PK;

PK - 是表中主键的列。

如果您没有主键，可以试试这个：

SELECT C1.CUSTOMER_FIRST_NAME,
  C1.CUSTOMER_LAST_NAME ,
  C2.CUSTOMER_FIRST_NAME,
  C2.CUSTOMER_LAST_NAME
FROM CUSTOMERS C1
INNER JOIN CUSTOMERS C2
ON C1.CUSTOMER_ZIP = C2.CUSTOMER_ZIP
WHERE C1.CUSTOMER_FIRST_NAME <> C2.CUSTOMER_FIRST_NAME
  AND C2.CUSTOMER_LAST_NAME <> C2.CUSTOMER_LAST_NAME

但是仍有一个问题，在你的输出中你会得到例如。

Mary Smith James Bond
James Bond Mary Smith

删除排列：

SELECT C1.CUSTOMER_FIRST_NAME,
  C1.CUSTOMER_LAST_NAME ,
  C2.CUSTOMER_FIRST_NAME,
  C2.CUSTOMER_LAST_NAME,
  C1.CUSTOMER_ZIP
FROM T_CUSTOMERS C1
LEFT JOIN T_CUSTOMERS C2
ON (C1.CUSTOMER_ZIP = C2.CUSTOMER_ZIP
    AND
    C1.CUSTOMER_NUMBER > C2.CUSTOMER_NUMBER );

另请参阅：SQL: self join using each rows only once

在Oracle Sql上使用不同条件在同一个表上列出对

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