pg的计算百分数的问题

SELECT
   cast("dept_id" as varchar(32)) , 

   cast("dept_name" as varchar(30)) AS "病区",
   "total_surgical_patients" AS "手术总数",
   "total_preop_medication_patients" AS "用药总数",
   "total_discharged_patients" AS "出院总数",

    CASE
        WHEN "total_surgical_patients" = 0 THEN NULL
        ELSE ROUND(("total_preop_medication_patients"/NULLIF("total_surgical_patients", 0))*100, 2)::varchar(20)
    END AS "按所在科室用药率%",
    CASE
        WHEN "total_discharged_patients" = 0 THEN NULL
        ELSE ROUND(("total_preop_medication_patients"/NULLIF("total_surgical_patients", 0))*100, 2)::varchar(20)
    END AS "按出院科室用药率%",

    cast("dept_parentcode" as varchar(40))

FROM "RemoteData"."fn_getantidruguse_surgery"('2021/3/1',  '2024/3/30', 'preoperative_medication', ' and 1=1 ')
order by "dept_id"

出现摸不着头脑的问题，是分母异常自动屏蔽处理了，导致计算百分数是0。因此需要检查分母NULLIF（）