出现原因，是因为在更新的的表和读取的表是同一个表。

  CREATE or replace TRIGGER T_userupdateT  BEFORE update  ON T_user  REFERENCING OLD AS old  NEW AS N_ROW   FOR EACH ROW DECLARE U_xtfidemp1 varchar(36);
 u_xtempcode1 varchar(20);
 u_xtempcodeCount int:=0; 
 U_xtfidempCount int:=0; 
 u_id1 int:=0; 
BEGIN 
  U_xtfidemp1:=:N_ROW.U_xtfidemp;
  u_xtempcode1:=:N_ROW.u_xtempcode;
  u_id1:=:N_ROW.u_id;
  select count(u_xtempcode) into u_xtempcodeCount from eas.T_user where u_xtempcode is not null and u_xtempcode=u_xtempcode1 and u_id<>u_id1;
  select count(U_xtfidemp) into U_xtfidempCount from eas.T_user where U_xtfidemp is not null and U_xtfidemp=U_xtfidemp1 and u_id<>u_id1;  
 IF u_xtempcodeCount>0 or U_xtfidempCount>0  THEN
         RAISE_APPLICATION_ERROR(-20001, 'eas.T_user u_xtempcode,U_xtfidemp,U_GZCode更新数据时有错误,有重复');
 END IF;
 end;

修改如下

  CREATE or replace TRIGGER T_userupdateT  BEFORE update  ON T_user  REFERENCING OLD AS old  NEW AS N_ROW   FOR EACH ROW DECLARE U_xtfidemp1 varchar(36); u_xtempcode1 varchar(20); u_xtempcodeCount int:=0;  U_xtfidempCount int:=0;  u_id1 int:=0; PRAGMA AUTONOMOUS_TRANSACTION;BEGIN   U_xtfidemp1:=:N_ROW.U_xtfidemp;  u_xtempcode1:=:N_ROW.u_xtempcode;  u_id1:=:N_ROW.u_id;  select count(u_xtempcode) into u_xtempcodeCount from eas.T_user where u_xtempcode is not null and u_xtempcode=u_xtempcode1 and u_id<>u_id1;  select count(U_xtfidemp) into U_xtfidempCount from eas.T_user where U_xtfidemp is not null and U_xtfidemp=U_xtfidemp1 and u_id<>u_id1;   IF u_xtempcodeCount>0 or U_xtfidempCount>0  THEN         RAISE_APPLICATION_ERROR(-20001, 'eas.T_user u_xtempcode,U_xtfidemp,U_GZCode更新数据时有错误,有重复'); END IF;COMMIT; end;