Question

table1
id, name, desc

1, Abc, some desc
2, Def, more desc
4, Jkl, another desc

table2 
id, table1_id, title
1,  1, My title
2,  1, Another title
3,  3, Yet another title

Table 1 has row with id of 3 “missing”. But if you notice, there is one refernece to this missing id in table2. So my question is how do I select all rows of table2 which has references to table1_id(s) which no longer are availabe in table1??

I am not very good at mysql queries and tried something like …
SELECT b.* FROM table2 b INNER JOIN table1 a ON b.table1_id != a.id and some others but could not get the desired result.

Could you throw some idea how this can be achieved?
Thanks

Answer 1

SELECT b.*
FROM table2 b
LEFT JOIN table1 a ON b.table1_id = a.id
WHERE a.id is null

Just some minor changes, from INNER to LEFT OUTER, with the condition that a.id is null (no match found in table a).

For deletes, use

DELETE FROM table2
WHERE table1_id not in (select id from table1)