oracle觸發器中判斷記錄是否為空白

我開始寫了一個觸發器，要判斷SSO_SP_LIST表中MASTER_SESS_ID欄位值與我要在SSO_MASTERS_INF
表中刪除的記錄的MASTER_SESS_ID欄位值相等的記錄是否為空白，我select了該記錄的MASTER_SESS_ID欄位，放入變數v（欄位MASTER_SESS_ID類型），判斷if v is not null，結果v為空白時，觸發器執行到這裡就出錯。

於是我將變數改為整型，讓它返回記錄的count值，判斷是否大於0,ok，觸發器照我的想法跑了，嘿嘿。

原來出錯的觸發器：

CREATE OR REPLACE TRIGGER TIG_BEF_DELETE_SSO_MASTERS
BEFORE DELETE
ON SSO_MASTERS_INF

FOR EACH ROW
DECLARE
   V SSO_SP_LIST.MASTER_SESS_ID%TYPE
BEGIN
   UPDATE SSO_MASTERS_HIS SET SSO_MASTERS_HIS.TIME_EXIT=SYSDATE WHERE SSO_MASTERS_HIS.MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
   SELECT MASTER_SESS_ID INTO V FROM SSO_SP_LIST WHERE SSO_SP_LIST.MASTER_SESS_ID=:OLD.MASTER_SESS_ID;

   IF V IS NOT NULL THEN
       DELETE FROM SSO_SP_LIST WHERE MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
       UPDATE SSO_SP_LIST_HIS SET TIME_SP_EXIT=SYSDATE WHERE MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
   END IF;
end TIG_BEF_DELETE_SSO_MASTERS;

修改後的觸發器

CREATE OR REPLACE TRIGGER TIG_BEF_DELETE_SSO_MASTERS
BEFORE DELETE
ON SSO_MASTERS_INF

FOR EACH ROW
DECLARE
   V int;
BEGIN
   UPDATE SSO_MASTERS_HIS SET SSO_MASTERS_HIS.TIME_EXIT=SYSDATE WHERE SSO_MASTERS_HIS.MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
   SELECT count(*) INTO V FROM SSO_SP_LIST WHERE SSO_SP_LIST.MASTER_SESS_ID=:OLD.MASTER_SESS_ID;

   IF V >0 THEN
       DELETE FROM SSO_SP_LIST WHERE MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
       UPDATE SSO_SP_LIST_HIS SET TIME_SP_EXIT=SYSDATE WHERE MASTER_SESS_ID=:OLD.MASTER_SESS_ID;
   END IF;
END TIG_BEF_DELETE_SSO_MASTERS;