PgSQL实现时间字段自动更新

CREATE OR REPLACE FUNCTION "public"."upd_update_time"()
  RETURNS "pg_catalog"."trigger" AS $BODY$
begin
    new.update_time= (SELECT to_char(now(),'YYYY-MM-DD HH24:MI:SS') now);
    return new;
end
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100

CREATE TABLE "sys_user" (
  "id" serial,
  "username" varchar(32) NOT NULL PRIMARY KEY,
  "password" varchar(128) NOT NULL,
  "secret" varchar(30) NOT NULL,
  "phone" varchar(11) DEFAULT NULL,
  "nickname" varchar(32) NOT NULL,
  "avatar" varchar(255) DEFAULT NULL,
  "status" enum_user_status NOT NULL,
  "reg_ip" varchar(15) DEFAULT NULL,
  "create_time" timestamp NOT NULL DEFAULT now(),
  "update_time" timestamp NOT NULL DEFAULT now(),
);