Oracle 更改字段的完美写法

declare
  sqlnum number;
  begin
  SELECT count(*) into sqlnum FROM USER_TAB_COLUMNS
  WHERE TABLE_NAME =upper('OPEN_SHOP_PRODUCT') and COLUMN_NAME='DESC_STATUS' and COLUMN_NAME='PIC_STATUS';
  if(sqlnum = 0) then
  execute immediate 'alter table OPEN_SHOP_PRODUCT add(DESC_STATUS NUMBER(4))';
  execute immediate 'comment on column OPEN_SHOP_PRODUCT.DESC_STATUS is ''文描发布状态：已发布0 未发布1''';
  execute immediate 'alter table OPEN_SHOP_PRODUCT add(PIC_STATUS NUMBER(4))';
  execute immediate 'comment on column OPEN_SHOP_PRODUCT.PIC_STATUS is ''图片发布状态：已发布0 未发布1''';
  end if ;
  dbms_output.put_line('增加成功！');
  end ;