SQL：在插入之前或更新之前有条件触发器

Question

I have a table:

Athlete :

Athlete_NO (PK) | Athlete_DOB |

and

Competes :

Athlete_NO (PFK) | Discipline_Code |

and

Discipline :

Discipline_Code (PK) | Discipline_Name |

I'm trying to write a trigger which won't allow the insertion of an Athlete under the age of 18 for certain disciplines Ex. Must be 18+ for Basketball

I'm using Oracle SQL Developer

Any help is appreciated (-:

The issue i'm facing is off incorporating "IF" under 18 for certain disciplines into the code.

Answer 1

try this but its not tested yet

CREATE OR REPLACE TRIGGER athlete_insert BEFORE
  INSERT ON ATHLETE FOR EACH ROW DECLARE athlete_too_young EXCEPTION;
  BEGIN
    IF ((new.athelt_Birthday BETWEEN new.athelt_Birthday(YEAR,-19, GETDATE()) AND new.athelt_Birthday(DAY,-365,GETDATE())) / 365.242 < 16) THEN
      RAISE athlete_too_young;
    END IF;
  EXCEPTION
  WHEN athlete_too_young THEN
    RAISE_APPLICATION_ERROR(-20000, 'Athlete must be older than 16');
  END;

Answer 2

You will need triggers on both the involved tables for the integrity constraint, namely Athlete and Competes.

In order to properly create this validation using a trigger a procedure should be created to obtain user-specified locks so the validation can be correctly serialized in a multi-user environment.

PROCEDURE request_lock
  (p_lockname                     IN     VARCHAR2
  ,p_lockmode                     IN     INTEGER  DEFAULT dbms_lock.x_mode
  ,p_timeout                      IN     INTEGER  DEFAULT 60
  ,p_release_on_commit            IN     BOOLEAN  DEFAULT TRUE
  ,p_expiration_secs              IN     INTEGER  DEFAULT 600)
IS
  -- dbms_lock.allocate_unique issues implicit commit, so place in its own
  -- transaction so it does not affect the caller
  PRAGMA AUTONOMOUS_TRANSACTION;
  l_lockhandle                   VARCHAR2(128);
  l_return                       NUMBER;
BEGIN
  dbms_lock.allocate_unique
    (lockname                       => p_lockname
    ,lockhandle                     => p_lockhandle
    ,expiration_secs                => p_expiration_secs);
  l_return := dbms_lock.request
    (lockhandle                     => l_lockhandle
    ,lockmode                       => p_lockmode
    ,timeout                        => p_timeout
    ,release_on_commit              => p_release_on_commit);
  IF    (l_return not in (0,4)) THEN
    raise_application_error(-20001, 'dbms_lock.request Failed ' || l_return);
  END IF;
  -- Must COMMIT an autonomous transaction
  COMMIT;
END request_lock;

This procedure can then be used in a trigger on each table eg

CREATE OR REPLACE TRIGGER competes_trg
AFTER INSERT OR UPDATE ON competes
FOR EACH ROW
DECLARE
  l_athlete_dob                  athlete.athlete_dob%TYPE; 
BEGIN
  request_lock('ATHLETE_AGE_' || :new.athlete_no);
  SELECT athelete_dob
  INTO l_athlete_dob
  FROM athlete
  WHERE athlete_no = :new.athlete_no;
  IF (  :new.discipline_code = 'BASKETBALL'
     AND (  l_athlete_dob IS NULL
         OR months_between(trunc(sysdate), l_athlete_dob)/12 < 18))
  THEN
    raise_application_error(-20000, 'Athlete must be 18 or over for Basketball');
  END IF;
END;

and

CREATE OR REPLACE TRIGGER athlete_trg
AFTER INSERT OR UPDATE ON athlete
FOR EACH ROW
DECLARE
  CURSOR csr_competes
  IS
  SELECT discipline_code
  FROM competes
  WHERE athlete_no = :new.athlete_no;
BEGIN
  request_lock('ATHLETE_AGE_' || :new.athlete_no);
  FOR r_compete IN csr_competes LOOP
    IF (  r_compete.discipline_code = 'BASKETBALL'
       AND (  :new.athlete_dob IS NULL
           OR months_between(trunc(sysdate), :new.athlete_dob)/12 < 18))
    THEN
      raise_application_error(-20000, 'Athlete must be 18 or over for Basketball');
    END IF;
  END IF;
END;

You can extend the IF condition to check for different ages for different disciplines.