Question

我正在尝试创建一个writers表，其中包含作者ID，姓氏，名字和ISBN，以及每个作者撰写的书名。使用与author和books表相同的数据类型，但不从这些表中复制数据。并且在作者表中包括作者ID作为主键，标题不为空，并且将ISBN作为引用ISBN的外键。但是我收到“违反了唯一约束（WT_PK）”错误：

CREATE TABLE writers
  (authorid VARCHAR2(4),
    lname VARCHAR2(10),
    fname VARCHAR2(10),
    isbn VARCHAR2(10),
    title VARCHAR2(30) CONSTRAINT title_nn NOT NULL,
    CONSTRAINT wt_pk PRIMARY KEY(authorid),
    CONSTRAINT wt_fk FOREIGN KEY(isbn) REFERENCES books(isbn));

INSERT INTO writers
SELECT authorid, fname, lname, isbn, title 
FROM author 
   JOIN bookauthor USING(authorid) 
   JOIN books USING(isbn);

Answer 1

似乎您需要为WRITERS表使用复合键。例（已在Oracle 12c和11g的dbfiddle here中进行了测试）：

-- 4 authors
create table author ( authorid primary key, fname, lname )
as
select 1, 'fname_1', 'lname_1' from dual union all
select 2, 'fname_2', 'lname_2' from dual union all
select 3, 'fname_3', 'lname_3' from dual union all
select 4, 'fname_4', 'lname_4' from dual ;

-- 7 books
create table books ( isbn primary key, title )
as
select '978-1449324451', 'title_1' from dual union all
select '978-1449324452', 'title_2' from dual union all
select '978-1449324453', 'title_3' from dual union all
select '978-1449324454', 'title_1_4' from dual union all 
select '978-1449324455', 'title_2_4' from dual union all
select '978-1449324456', 'title_3_4' from dual union all
select '978-1449324457', 'title_4_4' from dual ;

-- suppose that 4 books are written by one and the same author
create table bookauthor( authorid, isbn )
as
select A.authorid, B.isbn
from author A 
  join books B on A.authorid = substr( B.title, length( B.title ), 1 ) ;

向BOOKAUTHOR表添加一些约束，并检查其内容：

-- authorid, isbn
alter table bookauthor 
add (
  constraint ba_fk1 foreign key( authorid ) references author( authorid )
, constraint ba_fk2 foreign key( isbn ) references books( isbn )
, constraint ba_pk primary key ( authorid, isbn )
) ;


SQL> select * from bookauthor;
  AUTHORID ISBN          
---------- --------------
         1 978-1449324451
         2 978-1449324452
         3 978-1449324453
         4 978-1449324454
         4 978-1449324455
         4 978-1449324456
         4 978-1449324457

“原始” DDL代码（稍作修改）->插入失败

create table writers (
  authorid varchar2( 4 )
, lname varchar2( 10 )
, fname varchar2( 10 )
, isbn char( 14 )
, title varchar2( 30 ) constraint title_nn not null
, constraint wt_pk primary key ( authorid )
, constraint wt_fk foreign key( isbn ) references books( isbn )
);

INSERT INTO writers
SELECT authorid, fname, lname, isbn, title 
FROM author 
   JOIN bookauthor USING(authorid) 
   JOIN books USING(isbn);
-- ORA-00001: unique constraint (...WT_PK) violated 
-- author 4 with 4 books!

建议的DDL代码（和测试）：

create table writers2 (
  authorid varchar2( 4 )
, lname varchar2( 10 )
, fname varchar2( 10 )
, isbn char( 14 )
, title varchar2( 30 ) constraint title_nn2 not null
, constraint wt_pk2 primary key ( authorid, isbn )
, constraint wt_fk2 foreign key( isbn ) references books( isbn )
);

INSERT INTO writers2
SELECT authorid, fname, lname, isbn, title 
FROM author 
   JOIN bookauthor USING(authorid) 
   JOIN books USING(isbn);
-- 7 rows inserted.

从WRITERS2中选择

：

SQL> select * from writers2 ;

AUTH LNAME      FNAME      ISBN           TITLE                         
---- ---------- ---------- -------------- ------------------------------
1    fname_1    lname_1    978-1449324451 title_1                       
2    fname_2    lname_2    978-1449324452 title_2                       
3    fname_3    lname_3    978-1449324453 title_3                       
4    fname_4    lname_4    978-1449324454 title_1_4                     
4    fname_4    lname_4    978-1449324455 title_2_4                     
4    fname_4    lname_4    978-1449324456 title_3_4                     
4    fname_4    lname_4    978-1449324457 title_4_4

但是不确定为什么需要WRITERS表-因为您可以通过运行查询来生成其数据。

Answer 2

也许尝试一下：

.challenges input[type="checkbox"]:not(:checked) + label {
  color: lime;
}

.challenges input[type="checkbox"]:not(:checked) ~ input[type="checkbox"] + label {
  color: #000;
}

只需确保此行引用了您的作者表主键（现在是authorid）

<div class="challenges">
  <input type="checkbox">
  <label for="">test 01</label>
  <input type="checkbox">
  <label for="">test 02</label>
  <input type="checkbox">
  <label for="">test 03</label>
  <input type="checkbox">
  <label for="">test 01</label>
  <input type="checkbox">
  <label for="">test 02</label>
  <input type="checkbox">
  <label for="">test 03</label>
  <input type="checkbox">
  <label for="">test 01</label>
  <input type="checkbox">
  <label for="">test 02</label>
  <input type="checkbox">
  <label for="">test 03</label>
  <input type="checkbox">
  <label for="">test 01</label>
  <input type="checkbox">
  <label for="">test 02</label>
  <input type="checkbox">
  <label for="">test 03</label>
</div>

如果不需要，也删除唯一索引。在您的示例中，您可能不需要它，因为一位作者可以拥有多个书名。您应该阐明要完成的工作。

如何在从另一个表中提取数据时创建具有约束的表

2 个答案: