请教ORACLE的SELECT语句WITH READ ONLY的作用

请教ORACLE的SELECT语句WITH READ ONLY的作用

SELECT crac.HEADER_ID /*PK*/,
      crac.COST_GROUP_ID,
      crac.COST_TYPE_ID,
      crac.PERIOD_ID,
      crac.RCV_TRANSACTION_ID,
      crac.NET_QUANTITY_RECEIVED,
      crac.TOTAL_QUANTITY_INVOICED,
      crac.QUANTITY_AT_PO_PRICE,
      crac.TOTAL_INVOICE_AMOUNT,
      crac.AMOUNT_AT_PO_PRICE,
      crac.TOTAL_AMOUNT,
      crac.COSTED_QUANTITY,
      crac.ACQUISITION_COST,
      crac.PO_UNIT_PRICE,
      crac.PRIMARY_UOM,
      crac.REC_EXCHG_RATE /* FOREIGN KEYS RESOLVED */,
      ccg.cost_group,
      cct.cost_type,
      cpp.period_name,
      rt.TRANSACTION_TYPE,
      rt.TRANSACTION_DATE /* ID */,
      crac.PO_LINE_LOCATION_ID /* WHO */,
      crac.creation_date,
      crac.created_by,
      crac.last_update_date,
      crac.last_updated_by
  FROM CST_PAC_PERIODS  cpp,
      CST_COST_GROUPS  ccg,
      CST_COST_TYPES    cct,
      RCV_TRANSACTIONS  rt,
      CST_RCV_ACQ_COSTS crac
WHERE crac.PERIOD_ID = cpp.PAC_PERIOD_ID
  AND crac.cost_group_id = ccg.cost_group_id
  AND crac.cost_type_id = cct.cost_type_id
  AND crac.RCV_TRANSACTION_ID = rt.TRANSACTION_ID WITH READ ONLY

加了WITH READ ONLY 有什么作用

WITH READ ONLY
Specify WITH READ ONLY to indicate that the table or view cannot be updated. 这样等于通知ORALCE，只是查看，不做做更新。速度上会加快，不需要加锁。
 

建视图有三种模式：
1、默认的模式，就是什么也不加。
SQL code
--可以更新的
create or replace view view_a as
    select xxx from table_name;
--不可以可以更新的
create or replace view view_a as
    select xxx from table_name1 a,table_name2 b where a.xxx=b.xxx;
--还有很多种情况不允许更新呢，比如视图中用了distinct、group by 等

2、with read only 只读视图，不允许通过本视图更新本表
SQL code
create or replace view view_a as
    select xxx from table_name with read only;

3、with check option 允许通过视图更新本表，但是要check 视图的where条件。
SQL code
create or replace view view_a as
    select xxx from table_name where id < 10 with check option;

这种情况下，只能通过视图更新 id < 10 的数据，id >=10 的数据不允许更新。