[每日一题] OCP1z0-047 :2013-08-28 DELETE
[每日一题] OCP1z0-047 :2013-08-28 DELETE
正确答案:ACD
根据题库，操作如下：
A答案能删除：
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oe@OCM> delete from order_items
2 WHERE order_id IN (SELECT order_id FROM orders
3 WHERE 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*）
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oe@OCM> DELETE *
2 FROM order_items
3 WHERE order_id IN(SELECT order_id
4 FROM orders
5 WHERE orders
6 WHERE order_status IN(0,1));
DELETE *
*
ERROR at line 1:
ORA-00903: invalid table name
C答案能删除：
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oe@OCM> delete from order_items i
2 WHERE order_id=(SELECT order_id FROM orders o
3 WHERE i.order_id=o.order_id AND
4 order_status IN(0,1));
110 rows deleted.
oe@OCM> rollback;
Rollback complete.
D答案也能删除：
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oe@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.
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：
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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,
<span style="color:#ff0000;"> CONSTRAINT "ORDER_PK" PRIMARY KEY ("ORDER_ID")</span>
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 255
NOCOMPRESS 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：
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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,
<span style="color:#ff0000;">CONSTRAINT "ORDER_ITEMS_ORDER_ID_FK" FOREIGN KEY ("ORDER_ID")
REFERENCES "OE"."ORDERS" ("ORDER_ID") ON DELETE CASCADE ENABLE NOVALIDATE,</span>
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 255
NOCOMPRESS 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"
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删除了子表上的记录：
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oe@OCM> select count(*) from orders; －－主表
COUNT(*)
----------
105
oe@OCM> select count(*) from order_items; －－子表
COUNT(*)
----------
665
oe@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(*)
----------
105
oe@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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