For example, to delete rows that exist in t1 that have no match in t2, use a LEFT JOIN:
DELETE t1 FROM t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t2.id IS NULL;
This article is part of a series. You do not have to read them in order but I will be referring to topics and explanations in previous articles: Implementing Your Own Transactions with MVCCSQL Transaction Isolation Levels ExplainedImplementing Repeatable ...