Oracle 复合触发器 - 如何存储和“使用”已删除的行？按表索引？

Question

我现在正在为 Oracle 中的 DELETE 触发器进行长期斗争，该触发器在删除一行后，从剩余行中选择一个新的 MAX 值并将其写入另一个表。在偶然发现烦人的 ORA-04091 变异表错误（在 FOR EACH ROW 中无法读取表）之后，我切换到了 Oracle 的复合触发器。

如何最好地存储已删除的行（每行多个值，因为只有当删除的分数可能是高分，而不是较低分数时，进一步检查才会更新）？我担心，如果多个触发事件交叉触发，并且例如为“DeletedMatches”运行高分更新（该更新实际上并未被删除，而是由 Before 触发事件注册），则全局临时表可能会陷入混乱。

我可以创建一个表，a) 仅存在于该触发器中 b) 可以像普通数据库表或临时表一样在 SQL 中使用吗？

每当删除匹配项时，以下（伪）代码将更新 CurrentHighScores 表（旧的高分消失并被剩余的最高分取代）。

CREATE TABLE GameScores (
    MatchId number not null --primary key
    Player  varchar(255) not null,
    Game    varchar(255) not null, -- PacMan, Pong, whatever...
    Score   number not null );

-- High score for each game:
CREATE TABLE CurrentHighScores (
    HiScId number not null --primary key
    Player  varchar(255) not null,
    Game    varchar(255) not null,
    HighScore   number not null );

create or replace TRIGGER UpdHiScoreOnMatchDelete
FOR DELETE ON GameScores 
COMPOUND TRIGGER
    TYPE matchtable IS TABLE OF GameScores%ROWTYPE INDEX BY SIMPLE_INTEGER;
    DeletedMatches matchtable;
    MatchIndex SIMPLE_INTEGER := 0;

BEFORE EACH ROW IS -- collect deleted match scores
BEGIN
  MatchIndex:= MatchIndex+ 1;
  DeletedMatches(MatchIndex).Game := :old.Game;
  DeletedMatches(MatchIndex).Score := :old.Score;
  -- don't want to set every column value, want to 
      -- do like: INSERT :old INTO DeletedMatches;
      -- don't want the Index either!
END BEFORE EACH ROW;

AFTER STATEMENT IS
BEGIN
    UPDATE CurrentHighScores hsc 
    SET hsc.HighScore=(
      select max(gsc.Score) from GameScores gsc
      where hsc.Game=gsc.Game)
    where hsc.Game IN (
      select del.Game from DeletedMatches del where hsc.HighScore = del.Score)
      -- won't work, how can I check within the SQL if a row 
              -- for this game has been deleted, or anyhow integrate 
              -- DeletedMatches into the SQL, without a cursor?
              -- Optional further cond. in subselect, to update only 
              -- if deleted score equals highscore: 
    and exists(
      select 1 from GameScores where Game=hsc.Game); 
      -- ignore games without remaining match scores.

    -- Delete/set zero code for games without existing scores omitted here.
END AFTER STATEMENT;

Answer 1

“烦人的”变异表错误几乎总是表明设计不佳，通常是非规范化的数据模型。这似乎适用于本案。如果您需要维护聚合值、计数、最大值等，为什么不使用 Oracle 的内置功能呢？Oracle 为我们提供了专门用于处理摘要的 MATERIALIZED VIEW 对象。 了解更多。

在您的情况下，将 CurrentHighScores 替换为物化视图。

CREATE MATERIALIZED VIEW CurrentHighScores 
BUILD IMMEDIATE
REFRESH FAST
as select 
( 
    Player , 
    Game    , 
    max(score) as HighScore  
from GameScores 
group by player, game ; 

您还需要在 GameScore 上构建一个物化视图日志。