Question

我有如下表格：

语言

language_id   | language_name 
--------------------
   1             English
   2             Hindi

书

 book_id   | language_id  | book_name
---------------------------------
   1             1            Head First Java
   2             1            Head First C
   3             2            Head First Java
   4             2            Head First C

学生

 student_id   | language_id  |  book_id
--------------------------------------
   1             1                1
   2             2                3

现在，我必须更新book_id表格的Student列，其中包含当前id，新book_name = Head First Java和其他图书的book_name = Head First C值新书必须是同一种语言。

示例结果：

student_id   | language_id  |  book_id
--------------------------------------
   1             1                2
   2             2                4

我正面临着编写T-SQL查询来执行此操作的问题。请帮帮我。

Answer 1

认为您需要使用别名进行更新，以便在设置子查询中找到正确的语言。

update s
set s.book_id = (select book_id from book 
                 where book_name = 'Head First C'
                and language_id = s.language_id)
from student s
where s.book_id in (select book_id from book where book_name = 'Head First Java')

Answer 2

你必须通过这样的任何条件。

 update Student set book_id = 2 where book_id = 1

或

update Student set book_id = 2 where book_id = 1 and student_id = 1

Answer 3

请尝试一下，它应该符合您的要求

UPDATE s SET s.book_id = b.book_id
FROM [language] l
INNER JOIN (SELECT language_id, 
                MAX(book_id) book_id 
            FROM book 
            GROUP BY language_id ) b ON b.language_id = l.language_id 
INNER JOIN student s ON s.language_id = b.language_id

Answer 4

一种方法是加入书籍和语言表，并以此为基础进行更新如果假设Indi书的名字也用英文书写并且与英文版完全相同，那就没问题了。

但是如果您知道book_id和language_id，那么另一种方式可能是通过Student表上的几个简单的硬编码更新。

update Student set book_id = 2 where book_id = 1 and language_id = 1;
update Student set book_id = 4 where book_id = 3 and language_id = 2;

使用SQL Server中的选择查询更新列值的SQL查询

4 个答案: