Question

hopefully you can get what I want to do from the mysql query below.

delete d1 from 
D as d1, D as d2
left join C rel1 on rel1.tld_tod_id=d1.did
left join C rel2 on rel2.tld_tod_id=d2.did
where d1.did!=d2.did and d1.name=d2.name
and rel1.cid is null and rel2.cid is not null
;

I got unknown column d1.did in on clause,
how do I get it right?

Answer 1

Using as is for column aliases. For table aliases just put the alias behind the table

delete d1 from 
D d1, D d2
left join C rel1 on rel1.tld_tod_id=d1.did
left join C rel2 on rel2.tld_tod_id=d2.did
where d1.did!=d2.did and d1.name=d2.name
and rel1.cid is null and rel2.cid is not null
;

If I understand it right this will delete rows in the table D with a duplicate name if it has no relation with table C. However if that’s the case shouldn’t the joins have to be OUTER?