Question

我有四个表：Books，Magazine，Member和Transaction，每个表都有Title列。

图书表

BookId,   Title,           author,        edition,    no_of_books
1,        Harry Potter,    Jk rowling,    5,          11

杂志表：

MagazineId,    Title,      Publisher,    edition,   no_of_magazine
1,             filmfare,   bollywood,    5,         8

会员表：

MemberId,    name,    address,              contact,    email
4,           Arjun,   NO 56 park street,    071487845,  arjun56@gmail.com
8,           khan,    no 21 new lane pune,  07487547,   khan@gmail.com

当成员借用Book或Magazine时，Transaction表会保留记录（Trans_item_id为BookId或MagazineId）

例如：

交易表：

Trans_Id, Trans_Mem_Id, Trans_item_Id, Issue_date, Receive_date,Category
1, 4, 1,06-04-2016, 10-04-2016,book
2, 8, 1,08-04-2016, 11-04-2016,magazine

那么如何使用SQL从数据库中选择数据并向此显示顺序

例如：

Tran_id, Title, member name, issue date, receive date

谢谢。

Answer 1

试试这个：

SELECT t.tran_id,
  case when t.category = 'books' then b.title else t.title end AS title,
  u.name,
  t.issue_date,
  t.receive_date
FROM transaction t
INNER JOIN member u
ON t.trans_mem_id = u.memberid
LEFT JOIN books b
ON t.trans_item_id = b.bookid
AND t.category     = 'books'
LEFT JOIN magazines m
ON t.trans_item_id = m.magazineid
AND t.category     = 'magazines'

Answer 2

选择 t.trans_item_id为tran_id，合并（b.title，ma.title）， m.name，t.issue_date，t.receive_date 从交易内部联接成员m在m.memberid = t.trans_mem_id上离开加入 b上的书籍t.trans_item_id = b.bookid 离开加入杂志ma t.trans_item_id = ma.Magazineid

Answer 3

您需要再添加一个列，以确定借用的项目是书籍/杂志......

Select 
    t.Tran_ID,
    case 
       when t.type = 'book' 
         then 
            (select title from book where book.I'd = t.transitemid) 
         else 
            (select title from magazine where magazineid = t.tranitemid) 'title',
    m.member name, t.receivedate 
from 
    transaction t, membertable m 
where 
    t.Tranmemberid = m.memberid

如何从两个使用相同主键的表中获取数据

3 个答案: