Question

两个表是book_data＆amp; author_data。

book_data有3个字段= author_id，book_name，book_id。
author_data有5个字段= author_id，first_name，last_name，dob，social。

我可以在没有COUNT或HAVING的情况下运行：

SELECT first_name, last_name, book_data.author_id
FROM author_data INNER JOIN book_data
                 ON book_data.author_id = author_data.author_id
                 WHERE book_data.author_id = author_data.author_id;

当我添加：

GROUP BY author_id
HAVING COUNT (author_id) > 1)

我收到错误消息。

Answer 1

两件事：{1}当您使用JOIN和ON时，您不需要编写WHERE子句来连接表。 {2} GROUP BY返回＆＃34; ...每组的一行摘要信息＆＃34; （见documentation）

测试设置（Oracle 12c）

create table authors (
  author_id  number primary key
, first_name varchar2(64)
, last_name  varchar2(64)
, dob        date
, social     varchar2(4000) 
);

create table books (
  author_id references authors
, book_name  varchar2(256)
, book_id    number generated always as identity start with 5000
);

begin
  insert into authors ( author_id, first_name, last_name, dob, social )
    values ( 1, 'fname1', 'lname1', date'2001-01-01', 'social1') ;
  insert into authors ( author_id, first_name, last_name, dob, social )
    values ( 2, 'fname2', 'lname2', date'2002-02-02', 'social2') ;
  insert into authors ( author_id, first_name, last_name, dob, social )
    values ( 3, 'fname3', 'lname3', date'2003-03-03', 'social3') ;
end ;
/

begin
  insert into books ( author_id, book_name ) values ( 1, 'book1' );
  insert into books ( author_id, book_name ) values ( 2, 'book2' );
  insert into books ( author_id, book_name ) values ( 2, 'book22' );
  insert into books ( author_id, book_name ) values ( 3, 'book3' );
  insert into books ( author_id, book_name ) values ( 3, 'book33' );
  insert into books ( author_id, book_name ) values ( 3, 'book333' );
end;
/

我们现在有以下作者和书籍：

SQL> select * from authors;
AUTHOR_ID  FIRST_NAME  LAST_NAME  DOB        SOCIAL   
1          fname1      lname1     01-JAN-01  social1  
2          fname2      lname2     02-FEB-02  social2  
3          fname3      lname3     03-MAR-03  social3  


SQL> select * from books;
AUTHOR_ID  BOOK_NAME  BOOK_ID  
1          book1      5000     
2          book2      5001     
2          book22     5002     
3          book3      5003     
3          book33     5004     
3          book333    5005

{1}使用JOIN ... ON（无WHERE子句）

SQL> select 
  2    first_name
  3  , last_name
  4  , B.author_id
  5  from authors A
  6    join books B on B.author_id = A.author_id ;

FIRST_NAME  LAST_NAME  AUTHOR_ID  
fname1      lname1     1          
fname2      lname2     2          
fname2      lname2     2          
fname3      lname3     3          
fname3      lname3     3          
fname3      lname3     3

{2}将GROUP BY和HAVING添加到查询中。

select 
  first_name
, last_name
, B.author_id
from authors A
  join books B on B.author_id = A.author_id 
group by B.author_id
having count( B.author_id ) > 1
;
-- ORA-00979: not a GROUP BY expression

-- works: SELECTed columns are listed in the GROUP BY clause
SQL> select 
  2    first_name
  3  , last_name
  4  , B.author_id
  5  from authors A
  6    join books B on B.author_id = A.author_id 
  7  group by B.author_id, first_name, last_name
  8  having count( B.author_id ) > 1
  9  ;

FIRST_NAME  LAST_NAME  AUTHOR_ID  
fname2      lname2     2          
fname3      lname3     3

返回姓氏，作者姓名＆amp;写了多少本书大于1

1 个答案: