使用Window函数，您可以避免对不在GROUP BY中的每个列使用聚合函数

WITH CTE aS (  select rts.MERCH_DIV_NUM,
  rts.DEPT_NUM,
  ROW_NUMBER() OVER ( PARTITION BY bc.subject_code, bc.category_code, rts.ASSORTMENT_CODE ORDER BY  rts.DEPT_NUM ASC) rn
        , bc.subject_code, bc.category_code,
         rts.ASSORTMENT_CODE, rts.CURR_PEND_QTY, 
         rts.CURR_PEND_AMT, a.assortment_desc
  from rts_subcat_dept_pending rts
  inner join bn_assortment a on rts.assortment_code = a.assortment_code
  inner join bn_category bc on substr(rts.assortment_code, 0, 4) = bc.category_code      
) SELECT MERCH_DIV_NUM,DEPT_NUM,subject_code,category_code,ASSORTMENT_CODECURR_PEND_QTY
,CURR_PEND_AMT,assortment_desc FROM CTE WHERE rn = 1

您似乎希望使用分析函数而不是聚合：

select rts.MERCH_DIV_NUM,
       min(rts.DEPT_NUM)
         OVER (PARTITION BY bc.subject_code, bc.category_code, rts.ASSORTMENT_CODE)
         AS DEPT_NUM,
       bc.subject_code,
       bc.category_code,
       rts.ASSORTMENT_CODE,
       rts.CURR_PEND_QTY, 
       rts.CURR_PEND_AMT,
       a.assortment_desc
from   rts_subcat_dept_pending rts
       inner join bn_assortment a
       on rts.assortment_code = a.assortment_code
       inner join bn_category bc
       on substr(rts.assortment_code, 0, 4) = bc.category_code