   `sample_attribute_id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
   `sample_attribute_name` VARCHAR(30) NULL,
   `sample_attribute_value` VARCHAR(50) NULL,
-  `sample_id` INT UNSIGNED NULL,
+  `sample_id` INT UNSIGNED NOT NULL,
   PRIMARY KEY (`sample_attribute_id`),
   UNIQUE INDEX `sample_attribute_name_UNIQUE` (`sample_attribute_name` ASC),
   UNIQUE INDEX `sample_attributecol_UNIQUE` (`sample_id` ASC),
   CONSTRAINT `fk_sample_attribute_1`
     FOREIGN KEY (`sample_id`)
     REFERENCES `igfdb`.`sample` (`sample_id`)
-    ON DELETE SET NULL
+    ON DELETE CASCADE
     ON UPDATE CASCADE)
 ENGINE = InnoDB CHARSET=UTF8;
 

  CONSTRAINT `fk_project_attribute_1`
    FOREIGN KEY (`project_id`)
    REFERENCES `igfdb`.`project` (`project_id`)
    ON DELETE SET NULL
    ON UPDATE CASCADE)
ENGINE = InnoDB CHARSET=UTF8;


  `project_attribute_id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `project_attribute_name` VARCHAR(50) NULL,
  `project_attribute_value` VARCHAR(50) NULL,
  `project_id` INT UNSIGNED NOT NULL,
  PRIMARY KEY (`project_attribute_id`),
  UNIQUE INDEX `project_attribute_name_UNIQUE` (`project_attribute_name` ASC),
  INDEX `fk_project_attribute_1_idx` (`project_id` ASC),
