-- format_id in bank_import_batches nullable machen.
-- Beim Löschen eines Formats werden vorhandene Batches behalten; format_id wird NULL gesetzt.
ALTER TABLE bank_import_batches DROP FOREIGN KEY bank_import_batches_ibfk_1;
ALTER TABLE bank_import_batches MODIFY format_id INT UNSIGNED NULL;
ALTER TABLE bank_import_batches
    ADD CONSTRAINT fk_bib_format_id
    FOREIGN KEY (format_id) REFERENCES bank_import_formats(id) ON DELETE SET NULL;