比较相同 table 中的记录时如何避免 return 重复（A:B 和 B:A）

Question

我已经被这个问题困扰了一段时间，无法解决，非常感谢您的指导

我正在比较一个人 table 的记录，看看它们是否可能相同。为此，我使用 with 语句来获取我需要的值并查找匹配项

CREATE TABLE persons (
  serialno VARCHAR(20) NOT NULL,
  given VARCHAR(30) NOT NULL,
  family  VARCHAR(30) NOT NULL,
  dob  DATE NOT NULL,
  gender VARCHAR2(20 BYTE),
  address VARCHAR2(64 BYTE)
);

INSERT ALL 
    INTO persons ( serialno, given, family,dob,gender,address ) VALUES ( '001', 'Mick', 'Dundon','01/01/1970','Male','Main St' )
    INTO persons ( serialno, given, family, dob,gender,address) VALUES ( '002', 'Mick', 'Dundon','01/01/1970', 'Male','Montague St' )
    INTO persons ( serialno, given, family,dob,gender,address ) VALUES ( '003', 'Dave', 'Doyle', '13/10/1981','Male', 'Rathmines')
    INTO persons ( serialno, given, family,dob,gender,address ) VALUES ( '004', 'Jim', 'Morrison', '15/08/1956','Male','Newtown')
    INTO persons ( serialno, given, family, dob,gender,address) VALUES ( '005', 'Sam', 'Wise', '12/12/1992','Male','High St')
SELECT 1 FROM dual;

with rec as
(select serialno,given,family,dob,gender,address 
from persons)
select * 
from rec r1
join rec r2
on r1.given = r2.given
and r1.family = r2.family
and r1.gender = r2.gender
and r1.serialno <> r2.serialno

代码工作正常，除了我最终得到重复项，因为 R1 记录将在输出中进一步显示为 R2，反之亦然。
有没有一种简单的方法可以避免这种重复？

Answer 1

您可以使用解析 COUNT 函数获取所有没有 self-join 的重复项：

SELECT serialno, given, family, dob, gender, address
FROM   (
  SELECT serialno, given, family, dob, gender, address,
         COUNT(*)  OVER (PARTITION BY given, family, gender) AS num_matches
  FROM   persons
)
WHERE num_matches > 1;

如果您还想将值与具有相同 given/family/gender 组合和最小序列号的行进行比较，那么您可以再次避免 self-join 通过使用解析函数：

SELECT serialno, given, family, dob, gender, address,
       min_serialno, min_dob, min_address
FROM   (
  SELECT serialno,
         given,
         family,
         dob,
         gender,
         address,
         MIN(serialno) OVER (PARTITION BY given, family, gender) AS min_serialno,
         MIN(dob) KEEP (DENSE_RANK FIRST ORDER BY serialno)
           OVER (PARTITION BY given, family, gender) AS min_dob,
         MIN(address) KEEP (DENSE_RANK FIRST ORDER BY serialno)
           OVER (PARTITION BY given, family, gender) AS min_address
  FROM   persons
)
WHERE serialno > min_serialno;

如果在 Oracle 中，您想获得所有可能的组合，那么您可以使用分层查询来避免 self-join：

SELECT serialno, given, family, dob, gender, address,
       PRIOR serialno AS p_serialno,
       PRIOR dob      AS p_dob,
       PRIOR address  AS p_address
FROM   persons
WHERE  LEVEL = 2
CONNECT BY
       PRIOR gender   = gender
AND    PRIOR given    = given
AND    PRIOR family   = family
AND    PRIOR serialno < serialno

db<>fiddle here

比较相同 table 中的记录时如何避免 return 重复（A:B 和 B:A）

How to not return duplicates when comparing records in same table (A:B and B:A)

sql

duplicates

oracle-sqldeveloper

with-statement