How to delete a row when first row second column is same as second rows first column in sql

Question

How to delete a row if first row's code column equals to the second rows number column and second rows' code column equals to the first row's number column .

sql must not use loop

use this as sample code

CREATE TABLE #temp(id int, code int, Number int)

Insert into #temp values(1,2,1)
Insert into #temp values(2,1,2)
Insert into #temp values(3,2,3)
Insert into #temp values(4,2,3)
Insert into #temp values(5,2,3)

select * from #temp

Answer 1

Since you didn't specify what RDBMS you are using. Let me assume that it is SQL Server, then you can do this:

;WITH CTE
AS
(
   select * , ROW_NUMBER() OVER(ORDER BY ID) rownum
    from temp
), RowsToDelete
AS(
    SELECT c1.*
    FROM CTE c1
    INNER JOIN CTE c2 ON c1.rownum - c2.rownum = 1 AND c1.number = c2.code
)
DELETE r
FROM temp r
WHERE ID IN  ( SELECT ID 
               FROM RowsToDelete);

For the sample data, you posted this will delete only one row, which is:

ID     CODE    NUMBER 
2       1        2     

SQL Fiddle Demo

Answer 2

Simply use a join to get the rows you want to delete using the criteria you've specified:

delete t1
from #temp t1
inner join #temp t2
    on t1.code = t2.Number and t2.code = t1.Number

Answer 3

delete t1

from #temp t1

where exists(

select * from #temp t2

where t1.code = t2.Number and t2.code = t1.Number and t2.Id > t1.Id

)