ALTER TABLE `Invoice`
  ADD COLUMN `quotationId` VARCHAR(191) NULL;

CREATE UNIQUE INDEX `Invoice_quotationId_key`
  ON `Invoice`(`quotationId`);

ALTER TABLE `Invoice`
  ADD CONSTRAINT `Invoice_quotationId_fkey`
  FOREIGN KEY (`quotationId`)
  REFERENCES `Quotation`(`id`)
  ON DELETE SET NULL
  ON UPDATE CASCADE;