Mysql select 不同行不同列的相同值

Question

         new_id                                          old_id
         000                                              333
         111                                              666
         222                                              555
         333                                              777

I want to select the rows with the same values in old_id and new_id so my select should return row 1 and 4 from the example

SELECT *
 FROM `table` AS `t`
      INNER JOIN ( SELECT * FROM `table`  ) as `old`
      ON `old`.`old_id` = `t`.`new_id`

I have this query but it doesn't work it just returns all the records

Answer 1

Try this below logic-

SELECT DISTINCT C.* FROM 
(
    SELECT A.new_id
    FROM your_table A
    INNER JOIN your_table B ON A.new_id = B.Old_id
)A
INNER JOIN your_table C 
ON A.new_id = C.new_id
OR A.new_id = C.old_id

Answer 2

I would just use exists :

select t.*
from t
where exists (select 1
              from t t2
              where t2.new_id = t.old_id
             ) or
      exists (select 1
              from t t2
              where t2.old_id = t.new_id
             ) ;

In particular, this can take advantage of indexes on (old_id) and (new_id) . With those indexes, this should be the fastest solution.