Question

I’m using MySQL 5.5 with a complex schema that has foreign key constraints.

I want to execute multiple update and delete SQL statements.

After a subset of these statements have executed there may be foreign key constraint violations.

After all of these statements have executed there shouldn’t be foreign key constraint violations.

I know about cascade, I don’t want to use it because some of the changes require more complex logic.

My question is, is there a way to combine my multiple statements together (as a multi statement, transaction, etc) such that the foreign key constraints are not checked until after they are all completed? (And if there is an error than none of them are executed?)

Answer 1

MySQL does not implement deferred constraint checking. From the manual,

Deviation from SQL standards: Like MySQL in general, in an SQL
statement that inserts, deletes, or updates many rows, InnoDB checks
UNIQUE and FOREIGN KEY constraints row-by-row. When performing foreign
key checks, InnoDB sets shared row-level locks on child or parent
records it has to look at. InnoDB checks foreign key constraints
immediately; the check is not deferred to transaction commit.
According to the SQL standard, the default behavior should be deferred
checking. That is, constraints are only checked after the entire SQL
statement has been processed. Until InnoDB implements deferred
constraint checking, some things will be impossible, such as deleting
a record that refers to itself using a foreign key.

So there is no way to check constraints only at the end of a group of SQL statements.