[每日一题] OCP1z0-047 :2013-08-28   DELETE........................................................

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正确答案:ACD

根据题库，操作如下：
　
A答案能删除：

oe@OCM> delete from order_items 2WHERE order_id IN (SELECT order_id FROM orders 3WHERE order_status IN(0,1));110 rows deleted.oe@OCM> rollback;Rollback complete.

B答案不能删除：没有这样的语法（DELETE * FROM,即DELETE后直接跟表名，而不能用*）

oe@OCM> DELETE *2FROM order_items 3WHERE order_id IN(SELECT order_id 4FROM orders 5WHERE orders 6WHERE order_status IN(0,1)); DELETE ** ERROR at line 1: ORA-00903: invalid table name

C答案能删除：

oe@OCM> delete from order_items i 2WHERE order_id=(SELECT order_id FROM orders o 3WHERE i.order_id=o.order_id AND 4order_status IN(0,1));110 rows deleted.oe@OCM> rollback;Rollback complete.

D答案也能删除：

oe@OCM> delete from(select * from order_items i,orders o 2WHERE i.order_id=o.order_id AND order_status in(0,1)); 110 rows deleted.

　分析D能删除的原因：

　1、ORDERS表有主键ORDER_ID:CONSTRAINT "ORDER_PK" PRIMARY KEY ("ORDER_ID")。
　看下面红色字体：
　

oe@OCM> select dbms_metadata.get_ddl('TABLE','ORDERS') from dual;DBMS_METADATA.GET_DDL('TABLE','ORDERS') --------------------------------------------------------------------------------CREATE TABLE "OE"."ORDERS"("ORDER_ID" NUMBER(12,0), "ORDER_DATE" TIMESTAMP (6) WITH LOCAL TIME ZONE CONSTRAINT "ORDER_DATE_NN" NOT NULL ENABLE, "ORDER_MODE" VARCHAR2(8), "CUSTOMER_ID" NUMBER(6,0) CONSTRAINT "ORDER_CUSTOMER_ID_NN" NOT NULL ENABLE, "ORDER_STATUS" NUMBER(2,0), "ORDER_TOTAL" NUMBER(8,2), "SALES_REP_ID" NUMBER(6,0), "PROMOTION_ID" NUMBER(6,0),CONSTRAINT "ORDER_MODE_LOV" CHECK (order_mode in ('direct','online')) ENABLE,CONSTRAINT "ORDER_TOTAL_MIN" CHECK (order_total >= 0) ENABLE,CONSTRAINT "ORDER_PK" PRIMARY KEY ("ORDER_ID") USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS NOLOGGING STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT) TABLESPACE "EXAMPLE"ENABLE,CONSTRAINT "ORDERS_SALES_REP_FK" FOREIGN KEY ("SALES_REP_ID") REFERENCES "HR"."EMPLOYEES" ("EMPLOYEE_ID") ON DELETE SET NULL ENABLE,CONSTRAINT "ORDERS_CUSTOMER_ID_FK" FOREIGN KEY ("CUSTOMER_ID") REFERENCES "OE"."CUSTOMERS" ("CUSTOMER_ID") ON DELETE SET NULL ENABLE) SEGMENT CREATION IMMEDIATE PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255NOCOMPRESS NOLOGGING STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT) TABLESPACE "EXAMPLE"

2、ORDER_TIEMS表有外键ORDER_ID:CONSTRAINT "ORDER_ITEMS_ORDER_ID_FK" FOREIGN KEY ("ORDER_ID")
REFERENCES "OE"."ORDERS" ("ORDER_ID") ON DELETE CASCADE ENABLE NOVALIDATE,并加上了主外键可以级联删除。
看下面红色字体：

oe@OCM> select dbms_metadata.get_ddl('TABLE','ORDER_ITEMS') from dual;DBMS_METADATA.GET_DDL('TABLE','ORDER_ITEMS') --------------------------------------------------------------------------------CREATE TABLE "OE"."ORDER_ITEMS"("ORDER_ID" NUMBER(12,0), "LINE_ITEM_ID" NUMBER(3,0) NOT NULL ENABLE, "PRODUCT_ID" NUMBER(6,0) NOT NULL ENABLE, "UNIT_PRICE" NUMBER(8,2), "QUANTITY" NUMBER(8,0),CONSTRAINT "ORDER_ITEMS_PK" PRIMARY KEY ("ORDER_ID", "LINE_ITEM_ID") USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS NOLOGGING STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT) TABLESPACE "EXAMPLE"ENABLE,CONSTRAINT "ORDER_ITEMS_ORDER_ID_FK" FOREIGN KEY ("ORDER_ID") REFERENCES "OE"."ORDERS" ("ORDER_ID") ON DELETE CASCADE ENABLE NOVALIDATE,CONSTRAINT "ORDER_ITEMS_PRODUCT_ID_FK" FOREIGN KEY ("PRODUCT_ID") REFERENCES "OE"."PRODUCT_INFORMATION" ("PRODUCT_ID") ENABLE) SEGMENT CREATION IMMEDIATE PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255NOCOMPRESS NOLOGGING STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT) TABLESPACE "EXAMPLE"

删除了子表上的记录：
　　

oe@OCM> select count(*) from orders;　　　　－－主表COUNT(*) ----------105oe@OCM> select count(*) from order_items;　　－－子表COUNT(*) ----------665oe@OCM> delete from(select * from order_items i,orders o 2 WHERE i.order_id=o.order_id AND order_status in(0,1));110 rows deleted.oe@OCM> select count(*) from orders;　　　－－记录没变COUNT(*) ----------105oe@OCM> select count(*) from order_items;　　－－记录少了110条COUNT(*) ----------555 

有些人D答案百思不得期解，模拟这个操作时一直报错（ERROR at line 1:
ORA-01752: cannot delete from view without exactly one key-preserved table）原因就在于自己去建了两个表order和order_items时没有在这两个表上建约束主外键，并且加上主外键可以级联删除（CONSTRAINT "ORDER_ITEMS_ORDER_ID_FK" FOREIGN KEY ("ORDER_ID")　REFERENCES "OE"."ORDERS" ("ORDER_ID") ON DELETE CASCADE ENABLE NOVALIDATE）。
这个我就不再测试了，太简单了。

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