zoukankan      html  css  js  c++  java
  • OCP-1Z0-051-题目解析-第30题

    30. Evaluate the following CREATE TABLE commands: 
    CREATE TABLE orders 
    (ord_no NUMBER(2) CONSTRAINT ord_pk PRIMARY KEY, 
    ord_date DATE, 
    cust_id NUMBER(4)); 

    CREATE TABLE ord_items 
    (ord_no NUMBER(2), 
    item_no NUMBER(3), 
    qty NUMBER(3) CHECK (qty BETWEEN 100 AND 200), 
    expiry_date date CHECK (expiry_date > SYSDATE), 
    CONSTRAINT it_pk PRIMARY KEY (ord_no,item_no), 
    CONSTRAINT ord_fk FOREIGN KEY(ord_no) REFERENCES orders(ord_no));
     
    The above command fails when executed. What could be the reason?

     

    A. SYSDATE cannot be used with the CHECK constraint. 
    B. The BETWEEN clause cannot be used for the CHECK constraint. 
    C. The CHECK constraint cannot be placed on columns having the DATE data type. 
    D. ORD_NO and ITEM_NO cannot be used as a composite primary key because ORD_NO is also the FOREIGN KEY. 


    Answer: A
    题目问,上面建表语句运行失败的原因?
    A:sysdate不能用于check约束中(正确)

    SQL> create table t
      2  ( x date check (x >sysdate));
    ( x date check (x >sysdate))
                       *
    ERROR at line 2:
    ORA-02436: date or system variable wrongly specified in CHECK constraint
    

    B:Between子句不能用于check约束中(错误)
    SQL> create table t (x int check (x between 10 and 100));
    Table created.
    

    C:check约束不能放置在含有Date数据类型的字段 (错误)
    SQL> create table t ( x date check ( x > to_date('2014-01-12','YYYY-MM-DD')));
    Table created.

    D:ORD_NO and ITEM_NO不能被用作复合主键。由于ORD_NO同一时候也是外检(错误,一个字段能够同一时候被定义为主键和外检)
    SQL>create table ord_items
      2  (ord_no number not null,
      3  item_no number,
      4  constraint ord_fk foreign key(ord_no) references orders(ord_no),
      5  constraint it_pk primary key(ord_no,item_no));
     
    Table created.


  • 相关阅读:
    【开源我写的富文本】打造全网最劲富文本系列之技术选型
    【开源我写的富文本】打造全网最劲富文本技术选型之经典OOP仍是魅力硬核。
    Jquery会死吗?我为什么不用vue写富文本!
    JavaScript的因为所以
    JavaScript寻踪OOP之路
    JavaScript谁动了你的代码
    JavaScript神一样的变量系统
    JavaScript的前世今生
    ASPICE对追踪性和一致性要求
    ASPICE:能力等级评定
  • 原文地址:https://www.cnblogs.com/lcchuguo/p/5072464.html
Copyright © 2011-2022 走看看