关于一个Oracle触发器的有关问题了，不胜感谢

create or replace trigger Tig_CNOOC_ZJDC_MAXIMO_ONOFFafter insert or update on CNOOC_ZJDC_MAXIMO_ONOFFfor each rowdeclare _assetNo varchar2(100);declare _dateTime date;declare _tagName varchar2(400);declare _dataValue number(15,3);declare _type varchar2(10);declare _tableName varchar2(50);declare _tableColumn varchar2(50);declare _sql varchar2(2000);if inserting or updating then   _tagName:=:new.TAGID;   _dataValue:=:new.DATAVALUE;   _type:=:new.TYPE;   _assetNo:=:new.EQNUM;   _dateTime:=:new.DATETIME;      declare _cnt number;   _sql:='select count(TagName) into '||_cnt||',TagName into '||_tableName||',TableName into '||_tableColumn||' from DC_RALATIONSHIP_TAG where TagName='||_tagName||' and Type='||_type||'';   execute immediate _sql;      if _cnt>0 then        declare _num number;      _sql:='select count(*) into '||_num||' from '||_tableName||' where EQNUM='||_assetNo||' and DATETIME=todate('||_dateTime||','yyyy:MM:dd hh24:mi:ss')';      execute immediate _sql;      if _num=0 then                _sql:='insert into _tableName(EQNUM,DATETIME,'||_tableColumn||') values('||_assetNo||',todate('||_dateTime||','yyyy:MM:dd hh24:mi:ss'),'||_dataValue||')';         execute immediate _sql;      else               _sql:='update '||_tableName||' set '||_tableColumn||'='||_dataValue||' where EQNUM='||_assetNo||' and DATETIME=todate('||_dateTime||','yyyy:MM:dd hh24:mi:ss')';         execute immediate _sql;      end if   end if   end if