触发器在oracle sql中不起作用
我有一个名为Reading的表,有一个列调用ReaderID来指定谁读取读取。现在我想添加一个触发器,以便在表读取中添加新行时,始终检查读取器是否已经读取了5次。如果是,请不要进行插入。确保一个读者的阅读次数不能超过5次。这是我的代码,它不起作用,行仍然可以插入而无需检查触发器在oracle sql中不起作用,sql,oracle,triggers,Sql,Oracle,Triggers,我有一个名为Reading的表,有一个列调用ReaderID来指定谁读取读取。现在我想添加一个触发器,以便在表读取中添加新行时,始终检查读取器是否已经读取了5次。如果是,请不要进行插入。确保一个读者的阅读次数不能超过5次。这是我的代码,它不起作用,行仍然可以插入而无需检查 CREATE OR REPLACE TRIGGER TRIGGER1 BEFORE INSERT ON READING FOR EACH ROW DECLARE varReaderCount Int;
CREATE OR REPLACE TRIGGER TRIGGER1
BEFORE INSERT ON READING
FOR EACH ROW
DECLARE
varReaderCount Int;
varRID Int;
BEGIN
varRID := :new.ReaderID;
SELECT COUNT(*) INTO varReaderCount
FROM Reading
WHERE ReaderID = varRID;
IF (varReaderCount >= 5) THEN
BEGIN
DBMS_OUTPUT.PUT_LINE('*************************************************');
DBMS_OUTPUT.PUT_LINE('The reader has reach the limitation of reading.');
DBMS_OUTPUT.PUT_LINE('**************************************************');
RETURN;
END;
END IF;
END;
我不知道为什么。要阻止插入完成,您需要在触发器中引发异常。顺便说一句,那些DBMS_OUTPUT.PUT_LINE调用没有任何意义-触发器在Oracle内部运行,没有地方显示该输出。您需要替换这些行:
IF (varReaderCount >= 5) THEN
BEGIN
DBMS_OUTPUT.PUT_LINE('*************************************************');
DBMS_OUTPUT.PUT_LINE('The reader has reach the limitation of reading.');
DBMS_OUTPUT.PUT_LINE('**************************************************');
RETURN;
END;
END IF;
按顺序:
IF (varReaderCount >= 5) THEN
RAISE_APPLICATION_ERROR(-20101,'limitation of reading');
END IF;
在需要捕获异常以避免插入期间出错后:
DECLARE
readingException EXCEPTION;
PRAGMA EXCEPTION_INIT(readingException, -20101);
BEGIN
INSERT into READING VALUES (...);
EXCEPTION
WHEN readingException
THEN NULL;
END;
我假设您已经发现,您不能从定义行级触发器的同一个表中进行选择;它会导致表突变异常 为了使用触发器正确创建此验证,应创建一个过程以获取用户指定的锁,以便在多用户环境中正确序列化验证
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 = 1) THEN
raise_application_error(-20001, 'dbms_lock.request Timeout');
ELSIF (l_return = 2) THEN
raise_application_error(-20001, 'dbms_lock.request Deadlock');
ELSIF (l_return = 3) THEN
raise_application_error(-20001, 'dbms_lock.request Parameter Error');
ELSIF (l_return = 5) THEN
raise_application_error(-20001, 'dbms_lock.request Illegal Lock Handle');
ELSIF (l_return not in (0,4)) THEN
raise_application_error(-20001, 'dbms_lock.request Unknown Return Value ' || l_return);
END IF;
-- Must COMMIT an autonomous transaction
COMMIT;
END request_lock;
然后,此过程可以用于复合触发器(假设至少是Oracle 11),在早期版本中,需要将其拆分为单个触发器
CREATE OR REPLACE TRIGGER too_many_readings
FOR INSERT OR UPDATE ON reading
COMPOUND TRIGGER
-- Table to hold identifiers of inserted/updated readers
g_readerIDs sys.odcinumberlist;
BEFORE STATEMENT
IS
BEGIN
-- Reset the internal reader table
g_readerIDs := g_readerIDs();
END BEFORE STATEMENT;
AFTER EACH ROW
IS
BEGIN
-- Store the inserted/updated readers
IF ( INSERTING
OR ( UPDATING
AND :new.readerID <> :old.readerID))
THEN
g_readerIDs.EXTEND;
g_readerIDs(g_readerIDs.LAST) := :new.readerID;
END IF;
END AFTER EACH ROW;
AFTER STATEMENT
IS
CURSOR csr_readers
IS
SELECT DISTINCT
rid.column_value readerID
FROM TABLE(g_readerIDs) rid
ORDER BY rid.column_value;
CURSOR csr_constraint_violations
(p_readerID reading.readerID%TYPE)
IS
SELECT count(*) readings
FROM reading rdg
WHERE rdg.readerID = p_readerID
HAVING count(*) > 5;
r_constraint_violation csr_constraint_violations%ROWTYPE;
BEGIN
-- Check if for any inserted/updated reading there exists more than 5 readings
-- for the same reader. Serialise the constraint for each readerID so
-- concurrent transactions do not affect each other
FOR r_reader IN csr_readers LOOP
request_lock('TOO_MANY_READINGS_' || r_reader.readerID);
OPEN csr_constraint_violations(r_reader.readerID);
FETCH csr_constraint_violations INTO r_constraint_violation;
IF csr_constraint_violations%FOUND THEN
CLOSE csr_constraint_violations;
raise_application_error(-20001, 'Reader ' || r_reader.readerID || ' has ' || r_constraint_violation.readings || ' readings');
ELSE
CLOSE csr_constraint_violations;
END IF;
END LOOP;
END AFTER STATEMENT;
END;
这样的触发器不会停止超过5个会话插入行-每个会话只看到提交的数据,因此查询将只返回已提交的行。您可以有100个会话,所有插入行都不会触发触发器。除了已经指出的dbms_输出之外,触发器不做任何事情