如何在MySQL数据库中查找与其他行没有正确关联的行

Question

I have a table in my MySQL database that, in part, looks like this:

+----+-------+-------+
| id | owner | onwed |
+----+-------+-------+
|  1 |   A   |   B   |
|  2 |   B   |   A   |
|  3 |   C   |   D   |
|  4 |   D   |   C   |
|  5 |   E   |   X   |
+----+-------+-------+

They important feature here is that all the entries are paired, so that each "owner" is also "owned" by the record they correlate to. A "owns" B, and also B "owns" A. D "owns" C, and also C "owns" D.

However, in row 5,we have a problem. E "owns" X, but there is no entry for X "owning" E.

I need to be able to go through this table, which has thousands of records, and find all instances like row 5, where we have an orphaned record. Where there is no corralating with the "owner" and "owned" fields having a matched opposite. Also, there is no assurance that paired rows will follow each other as they do in my example.

This problem goes way beyond my MySQL abilities. I know how to do a search when I know what the value I'm looking for is. But I don't know how to go through each row one by one, take values out, and then use those values to do another search. I hope someone can help me out and I apologize that I'm so clueless on this matter that I don't have any code to suggest.

I'm not so worried about efficiency, in that this is a check I would only run every now and again when there is reason to suspect a problem. Also, if it helps, I manage my MySQL database from a PHP script, so if there is PHP code that can be leveraged to make the task more manageable, that could also be utilized.

Answer 1

What you need is a join . If you join the table on itself with the owned on owner.

SELECT T1.Id, T1.Owner, T1.Owned, T2.Id, T2.Owner, T2.Owned 
FROM tablename T1 
LEFT JOIN tablename T2
ON T1.Owned = T2.Owner
WHERE T2.Owned != T1.Owner
OR T2.Id IS NULL

Try to run the query without the WHERE clause to see what this join does. You get both owners and owned on a single row and then you can compare if they match.

Answer 2

You could try a query similar to (not sure about the backquotes of MySQL)

SELECT * FROM `table` 
  WHERE (`owner`,`owned`) 
  NOT IN (SELECT `owned`,`owner` FROM `table`);

There are probably cleaner solutions without selfjoins

Answer 3

There are better ways, but this will work:

SELECT
    *
FROM
    table
WHERE
    id NOT IN (
        SELECT
            id
        FROM
            table s1
        WHERE
            s1.owner = (
                    SELECT
                        onwed
                    FROM
                        table s2
                    WHERE
                        s2.onwed = s1.owner
            )
    );

Answer 4

Its easy:

select t1.id from tableName as t1 left join tableName as t2 
    on t1.owner = t2.owned and t1.owned = t2.owner 
    where t2.id is null

Answer 5

select 
    * 
from 
    mytable 

where id not in (
    select
        m1.id
    from
        mytable m1,
        mytable m2

    where 
        m1.owner=m2.owned    
)   

Answer 6

You can try this- demo below :

http://sqlfiddle.com/#!2/0db47/7

Answer 7

SELECT  a.id, a.owner, a.onwed
FROM    TableName a
        LEFT JOIN TableName b
          ON  (a.Owner = b.Owner AND a.Onwed = b.OnWed) OR
              (a.Owner = b.OnWed AND a.Onwed = b.Owner)
GROUP   BY  a.id, a.owner, a.onwed
HAVING  COUNT(*) = 1

• SQLFiddle Demo