code: protected Collection<String> getFKAddingScripts()
     {
        List<String> scripts = new ArrayList<String>();
  
        String constraintName =
           "JCR_FK_" + itemTableSuffix + "_PARENT FOREIGN KEY(PARENT_ID) REFERENCES " + itemTableName + "(ID)";
        scripts.add("ALTER TABLE " + itemTableName + " ADD CONSTRAINT " + constraintName);
  
        return scripts;
     }
docs: Returns SQL scripts for adding FK on JCR_ITEM table.