Question

我正在创建一个数据库来模拟游戏行业，它有两个看起来像这样的表：

PLAYABLE (Which games are playable on which consoles)
--------------------------------------------------
|  Game_ID (int)   | Console_Name (varchar(255)) | (both primary/foreign)
--------------------------------------------------

 CONSOLE
--------------------------------------------------
|  Console_Name (PK) |     Exclusives (int)      |
--------------------------------------------------

exclusives属性给出了控制台的游戏数量，只有控制台的游戏数量。

所以当我在“可播放的”中插入一个新的元组时关系，如果那是＆＃39; Game_ID＆＃39;已经存在过一次，那么我需要减少“排他性”。属性与相应的＆＃39; Console_Name。＆＃39;同样，如果它不存在，那么我会增加该控制台的独家数量。

我是Oracle新手，这是我尝试为此创建触发器：

CREATE OR REPLACE TRIGGER Exclusives_Count
    BEFORE INSERT ON Playable
    FOR EACH ROW
BEGIN
    DECLARE
        Game_Count NUMBER;
        Obsolete_Exclusive_Console VARCHAR(255);
    SELECT COUNT(Game_ID) INTO Game_Count FROM Playable WHERE Game_ID = :NEW.Game_ID;
    IF Game_Count = 0
    THEN 
        UPDATE Console
        SET Exclusives = Exclusives + 1
        WHERE Console.Console_Name = :NEW.Console_Name;
    ELSIF Game_Count = 1
    THEN
        SELECT Console_Name INTO Obsolete_Exclusive_Console FROM Playable WHERE Game_ID = :NEW.Game_ID;

        UPDATE Console
        SET Exclusives = Exclusives - 1
        WHERE Console.Console_Name = Obsolete_Exclusive_Console;
    END IF;
END;
/

输入此内容即表示“警告：使用编译错误创建触发器”＃34;但我不确定自己哪里出错了。

Answer 1

declare应该在代码中begin之前见下面的声明：

create table Playable(Game_ID int, Console_Name varchar(255));
create table CONSOLE(Console_Name  varchar(255), Exclusives int);
SQL> 
SQL> CREATE OR REPLACE TRIGGER Exclusives_Count
  2      BEFORE INSERT ON Playable
  3      FOR EACH ROW
  4  
  5  DECLARE
  6          Game_Count NUMBER;
  7          Obsolete_Exclusive_Console VARCHAR(255);
  8  BEGIN
  9  
 10      SELECT COUNT(Game_ID) INTO Game_Count FROM Playable WHERE Game_ID = :NEW.Game_ID;
 11      IF Game_Count = 0
 12      THEN
 13          UPDATE Console
 14          SET Exclusives = Exclusives + 1
 15          WHERE Console.Console_Name = :NEW.Console_Name;
 16      ELSIF Game_Count = 1
 17      THEN
 18          SELECT Console_Name INTO Obsolete_Exclusive_Console FROM Playable WHERE Game_ID = :NEW.Game_ID;
 19  
 20          UPDATE Console
 21          SET Exclusives = Exclusives - 1
 22          WHERE Console.Console_Name = Obsolete_Exclusive_Console;
 23      END IF;
 24  END;
 25  /

Trigger created

SQL> show errors
No errors for TRIGGER SCM.EXCLUSIVES_COUNT

SQL>

创建Oracle触发器以根据其在另一个表中的唯一性来递增/递减属性

1 个答案: