创建触发器以在表上实现排名

Question

我从未在 SQL Server 2008 中使用过触发器。所以我不知道如何去做。

我有一个游戏应用程序，我正在跟踪所玩问题的数量和正确回答的问题总数。我还节省了每个问题的平均时间。

现在我想根据正确答案的百分比记录排名，如果出现平局，我们将检查所用时间。我必须使用触发器来完成所有这些操作。

  id   | playerID | CompetitionID  | NoOfCOrrectANswers | NoOfPlayedQuestions | TimeTaken 
-----------------------------------------------------------------------------------------
  1      3             203              4                       8                  8.4
  2      56            203              9                      18                 13
  3      67            203              16                     45                 15

感谢任何帮助。提前致谢。

Answer 1

您可能不应该走这条路，因为更新的数量会很高。您可以将row_number() 或rank() 函数添加到显示比赛结果的查询中。

话虽如此，如果您觉得绝对必须在表格中保留排名信息，请添加一列

alter table ATable add PlayerRank int

并在 ATable 上创建触发器

create trigger RankingTrigger on ATable
after insert, update, delete
as
-- We don't want queries in a trigger to mess up with "Rows affected"
   set nocount on
-- If any of the following columns are mentioned in a query
-- Always true for insert and delete, but we will save updates
-- if we skip processing when columns participating in ranking 
-- are not changed
   If update (NoOfCOrrectANswers)
      OR update(NoOfPlayedQuestions)
      OR update(TimeTaken)
   begin
      -- CTE that returns primary key and rank by competition.
      -- I've changed your condition (percent of correct answers)
      -- As it would rank players with one correct answer over those
      -- who answered 100 questions and got only one wrong. If you
      -- want to change it, replace NoOfCOrrectANswers with 
      -- NoOfCOrrectANswers / NoOfPlayedQuestions
      ; with theRank as (
        select ID, row_number() over (partition by CompetitionID
                                      order by NoOfCOrrectANswers DESC,
                                               TimeTaken DESC) rn
          from ATable
      -- Only changed competitions
         where CompetitionID in
      -- Inserted table is available in trigger and OUTPUT clause
      -- of insert, update, delete statements.
      -- It contains newly added/changed rows
      -- We are using it here to filter only changed competitions
      -- Similary, Deleted table hold a copy of removed rows for delete 
      -- and old values for update
         (
            select CompetitionID
              from Inserted
            union
            select CompetitionID
              from Deleted
         )
      )
      update ATable
      -- Update to rank from theRank CTE
         set PlayerRank = theRank.rn
        from ATable
        -- All records participation in affected competitions
          inner join theRank
             on ATable.ID = theRank.ID
        -- Only change if really changed
        -- This part is very likely not needed. I have never tested
        -- to see if it affects performance
            and isnull(ATable.PlayerRank, 0) <> theRank.rn
   end