Question

I have 2 tables Table_A and Table_B. Table_A is a parent of Table_B. Table_B has 2 columns which refer to Table_A(I Mean both the columns refer to a column in Parent).

Table_A contains following columns (id,name,className)
Table_B contains following column (source,destination) both the columns refer to id in Table_A

Assume that Table_A contains the following data

id     name    className 
---------------------------
1       N1      C1 
2       N2      C2
3       N3      C3
4       N4      C4
5       N5      C6

Table_B

Source  Destination
------------------
1        2
2        3
3        4
3        5

I need a query where I require all Ids present in the Destination and not in Source and I need to join this Ids with Table_A to get name and className.

For the data I have shown the query should retrieve the following rows.

4     N4   C4
5     N5   C5

BTW here I have shown partial data but Table_B has more than 1000 records.

EDIT

I have written the following query but it was showing wrong results

select * from Table_A where id not in (select distinct Source from Table_B)

But it was giving right results currently but on long run we may face performance issue and also query retrieves data which is not present in both Source and Destination.

Answer 1

I only have SQLite installed, but this short query did the job:

SELECT table1.id, table1.name
FROM table1, table2
WHERE table2.destination NOT IN
        (SELECT DISTINCT source FROM table2)
AND table1.id=table2.destination;

-- Result:
-- 4|N4
-- 5|N5

EDIT: Of course it would be interesting to see a performance comparison with other solutions.