在Oracle Sql数据库上触发

Question

I have some issues to resolve on my sql database:

• ensure that a player can only have 2 yellow cards or one red
• a team can not have more than 5 foreign players (player who nationality is differet from French)

My model is something like that:

Team
-------
team_id (PK)
name

Player
-------
player_id (PK)
team_id (FK)
name
number_yellow_cards
number_red_cards
nationality

I think that trigger can resolve my problems. Here is my trigger, but doesn't work in any situation (insert/update)

create or replace TRIGGER foreign_players
Before Insert OR UPDATE on Player
FOR EACH ROW 
DECLARE nr_foreign_players INTEGER;
Begin

  IF INSERTING THEN
    SELECT Count(*) INTO nr_foreign_players
    FROM
        Team T
        INNER JOIN Player P ON P.team_id = T.team_id
    WHERE 
        P.team_id =  :new.team_id 
        AND P.nationality <> 'French';

    if(nr_foreign_players > 5) then
        Raise_Application_Error(-20000,'Error insert' ); 
    End If;
  END IF; --INSERTING

  IF UPDATING THEN
    SELECT Count(*) INTO nr_foreign_players
    FROM
        Team T
        INNER JOIN Player P ON P.team_id = T.team_id
    WHERE 
        P.team_id =  :new.team_id 
        AND P.nationality <> 'French';

    if(nr_foreign_players > 5) then
    Raise_Application_Error(-20000,'Error update' ); 
    End If;
  END IF; --UPDATING


End;

Anyone can help me?

Answer 1

This can't a 100% sure answer, as you did not exactly tell us what doesn't work in any situation .

I see several issues with your trigger :

1. The logic to ensure that a team can not have more than 5 non-French players seems correct, however why do you duplicate it for INSERT and UPDATE ? This can be simplified.

2. You are not at all verifying that a player can only have 2 yellow cards or one red

Here is an updated SQL code that should get the work done. It is performing each check one by one, raising application exception as soon as one check fails. No distinction is made between INSERT and UPDATE operations, as the logic is exactly the same for both operations.

CREATE OR REPLACE TRIGGER foreign_players
BEFORE INSERT OR UPDATE ON Player
FOR EACH ROW 
DECLARE 
    nr_foreign_players INTEGER;
BEGIN

    IF NVL(:new.number_yellow_cards, 0) > 2 THEN
        Raise_Application_Error(-20000, 'Too many yellow cards' ); 
    END IF;

    IF NVL(:new.number_red_cards, 0) > 1 THEN
        Raise_Application_Error(-20000, 'Too many red cards' ); 
    END IF;

    SELECT Count(*) INTO nr_foreign_players
    FROM
        Team T
        INNER JOIN Player P ON P.team_id = T.team_id
    WHERE 
        P.team_id =  :new.team_id 
        AND P.nationality <> 'French';
    IF nr_foreign_players > 5 THEN
        Raise_Application_Error(-20000, 'Too many foreign players' ); 
    END IF;

END;