T-SQL（一）遊標嵌套查詢

數據源
pubs 示例數據庫

目標
利用遊標用於生成作者出版情況報表，形式如下：

-------- Authors report --------
 
----- Books by Author: AuthorName1
         BookName1
         BookName2
 
----- Books by Author: AuthorName2
         BookName1
         BookName2

實現

-- 使用遊標

begin

  print('-------- Authors report --------')

  -- 聲明存儲作家信息的變量
  declare @au_name varchar(20), @au_lname varchar(20), @au_fname varchar(20),
    @au_id varchar(20)

  -- 聲明作家遊標
  declare c_author_name cursor
  for select au_lname, au_fname from authors
  declare c_author_id cursor
  for select au_id from authors

  -- 打開作家遊標
  open c_author_name
  open c_author_id

  -- 重置全局變量 @@fetch_status
  fetch next from c_author_id into @au_id
  fetch next from c_author_name into @au_lname, @au_fname

  -- 作家層循環
  while @@fetch_status = 0
    begin

        -- 拼接作家名稱
        set @au_name = @au_lname + ' ' + @au_fname

        print '----- Books by Author:' + @au_name

        -- 書號
        declare @book_id varchar(20)

        -- 書號遊標
        declare c_book_id cursor
        for select title_id from titleauthor where au_id = @au_id

        open c_book_id

        fetch next from c_book_id into @book_id

        -- 書號層循環
        while @@fetch_status = 0

          begin

            -- 書名
            declare @book_name varchar(20)

            -- 書名遊標
            declare book_name cursor
            for select title from titles where title_id = @book_id

            open book_name

            fetch from book_name into @book_name

            print @book_name

            close book_name

            deallocate book_name

            fetch next from c_book_id into @book_id

          end

        close c_book_id

        deallocate c_book_id

        fetch next from c_author_id into @au_id
        fetch next from c_author_name into @au_lname, @au_fname

    end

  -- 關閉作家遊標
  close c_author_id
  close c_author_name

  -- 釋放作家遊標
  deallocate c_author_id
  deallocate c_author_name

end


-- 不使用遊標
select au_lname, au_fname, title
from authors, titleauthor, titles
where authors.au_id = titleauthor.au_id and titles.title_id = titleauthor.title_id