Finding children with no parents

[bulrush]

I have a parent table called "group" where the key is an auto increment field called "grid". It is linked to child tables "parts" and "features", which both store the "grid" value in a field called "grid", linking them to the "group" table.

 

How do I find records in the "parts" and "features" tables where the record in "group" (the grid value) no longer exists? (Due to a possible bug, perhaps.)

 

 

[ignace]

SELECT ..

FROM group

RIGHT JOIN parts USING (grid)

RIGHT JOIN features USING (grid)

WHERE group.grid IS NULL

[bulrush]

And so the DELETE statement would be similar, like this?

DELETE FROM group
RIGHT JOIN parts USING (grid)
RIGHT JOIN features USING (grid)
WHERE group.grid IS NULL

 

[ignace]

Yes. Although before executing you may want to try this on a test database.