有谁帮我解释一下该表中各字段的含义?谢谢高手指点!CREATE TABLE insured_autos ( policy_id NUMBER CONSTRAINT policy_fk REFERENCE policies(policy_id ON DELETE CASCADE,vin VARCHAR2(40),coverage_begin DATE,coverage_term NUMBER,make
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![有谁帮我解释一下该表中各字段的含义?谢谢高手指点!CREATE TABLE insured_autos ( policy_id NUMBER CONSTRAINT policy_fk REFERENCE policies(policy_id ON DELETE CASCADE,vin VARCHAR2(40),coverage_begin DATE,coverage_term NUMBER,make](/uploads/image/z/14045227-43-7.jpg?t=%E6%9C%89%E8%B0%81%E5%B8%AE%E6%88%91%E8%A7%A3%E9%87%8A%E4%B8%80%E4%B8%8B%E8%AF%A5%E8%A1%A8%E4%B8%AD%E5%90%84%E5%AD%97%E6%AE%B5%E7%9A%84%E5%90%AB%E4%B9%89%3F%E8%B0%A2%E8%B0%A2%E9%AB%98%E6%89%8B%E6%8C%87%E7%82%B9%21CREATE+TABLE+insured_autos+%28++++policy_id+NUMBER+CONSTRAINT+policy_fk+REFERENCE+policies%28policy_id+ON+DELETE+CASCADE%2Cvin+VARCHAR2%2840%29%2Ccoverage_begin+DATE%2Ccoverage_term+NUMBER%2Cmake)
有谁帮我解释一下该表中各字段的含义?谢谢高手指点!CREATE TABLE insured_autos ( policy_id NUMBER CONSTRAINT policy_fk REFERENCE policies(policy_id ON DELETE CASCADE,vin VARCHAR2(40),coverage_begin DATE,coverage_term NUMBER,make
有谁帮我解释一下该表中各字段的含义?谢谢高手指点!
CREATE TABLE insured_autos (
policy_id NUMBER CONSTRAINT policy_fk REFERENCE policies(policy_id ON DELETE CASCADE,vin VARCHAR2(40),coverage_begin DATE,coverage_term NUMBER,make VARCHAR2(30),model VARCHAR(30),year NUMBER,CONSTRAIN auto_fk FROEIGN KEY (make,model,year) REFERENCES automobiles (make,model,year) ON DELETE SET NULL);
其中,各个字段的含义是什么啊? 请高手指教!多谢!
请问vin是哪个单词的缩写啊?肯定表示供应商么?
coverage_begin,日期 coverage_term,数字 这两个字段的含义有代表什么呢?
有谁帮我解释一下该表中各字段的含义?谢谢高手指点!CREATE TABLE insured_autos ( policy_id NUMBER CONSTRAINT policy_fk REFERENCE policies(policy_id ON DELETE CASCADE,vin VARCHAR2(40),coverage_begin DATE,coverage_term NUMBER,make
(1)表policies(策略)有以下字段:
policy_id,策略ID,数字
ON DELETE CASCADE
指定如果试图删除某行,而该行含有由其它表的现有行中的外键所引用的键,则也将删除所有包含那些外键的行.如果在目标表上也定义了级联引用操作,则对从那些表中删除的行同样采取指定的级联操作.
vin,供应商,变长字符串,40字节
coverage_begin,日期
coverage_term,数字
make,变长字符串,30字节
model,变长字符串,30字节
year,数字
(2)表automobiles(汽车)有以下字段:(猜的)
make制造厂家,变长字符串,30字节
model型号,变长字符串,30字节
year年代,整数
(3)表insured_autos 有以下字段:
policy_id,策略ID,数字
三个表的关系如下:
automobiles为静态基表,
policies表引用automobiles,关联字段为(make,model,year)
insured_autos关联policies,通过policy_id
好像是作汽车保险的程序.
本语句是SQL SERVER 2000的.
补充:
vin是哪个单词的缩写啊?肯定表示供应商么?
--不一定.猜的.要说由表定义完全猜到设计者的意图,那是不可能的.举例来说:name(姓名)字段你也可以放一个家具的名字啊.
coverage_begin,日期 coverage_term,数字 这两个字段的含义有代表什么呢?
--开始日期,及延续时段(天),同样,这也只是猜测.
另外.