Update with subqueries tuning help

Question

I have the following update that does the required job, but undersdtandably it is running really slowly.
update com_mat_stores
set MST_QTY_ISS_TY =  (SELECT NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_NO_UNITS) ,
                                                               '20',  DECODE(SUBSTR(COST_NO_UNITS,1,1), '-', COST_NO_UNITS, COST_NO_UNITS*-1),
                                                               '21',  COST_NO_UNITS)),0) STK_QTY
                                    FROM COM_COSTS WHERE COST_COST_YEAR = 2009
                                    AND COST_MST_ID = MST_ID AND ((COST_CSY_COSTEL = '23' AND COST_TRANS_CODE = 'M')
                                    OR (COST_CSY_COSTEL IN ('20','21')))),
    MST_VAL_ISS_TY = (SELECT NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_VALUE) ,
                                                                     '20',  DECODE(SUBSTR(COST_VALUE,1,1), '-', COST_VALUE, COST_VALUE*-1),
                                                                     '21',  COST_VALUE)),0) STK_VAL
                                    FROM COM_COSTS WHERE COST_COST_YEAR = 2009
                                    AND COST_MST_ID = MST_ID AND ((COST_CSY_COSTEL = '23' AND COST_TRANS_CODE = 'M')
                                    OR (COST_CSY_COSTEL IN ('20','21'))))
where  MST_QTY_ISS_TY <>  (SELECT NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_NO_UNITS) ,
                                                               '20',  DECODE(SUBSTR(COST_NO_UNITS,1,1), '-', COST_NO_UNITS, COST_NO_UNITS*-1),
                                                               '21',  COST_NO_UNITS)),0) STK_QTY
                                    FROM COM_COSTS WHERE COST_COST_YEAR = 2009
                                    AND COST_MST_ID = MST_ID AND ((COST_CSY_COSTEL = '23' AND COST_TRANS_CODE = 'M')
                                    OR (COST_CSY_COSTEL IN ('20','21')))) 
OR  MST_VAL_ISS_TY <> (SELECT NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_VALUE) ,
                                         '20',  DECODE(SUBSTR(COST_VALUE,1,1), '-', COST_VALUE, COST_VALUE*-1),
                                         '21',  COST_VALUE)),0) STK_VAL
                                    FROM COM_COSTS WHERE COST_COST_YEAR = 2009
                                    AND COST_MST_ID = MST_ID AND ((COST_CSY_COSTEL = '23' AND COST_TRANS_CODE = 'M')
                                        OR COST_CSY_COSTEL IN ('20','21')));I managed to get a select for the records changed to use an inline view and this is much faster (see below), but I cannot get this select translated into a update statement. Any help or ideas how to change this. The 2 tables in question are quite large COM_MAT_STORES has 34k and com_costs has 90k that match the criteria (7 million in total). I have checked
SELECT MST_ID, MST_MAT_STOCK_CODE, MST_STO_CODE, MST_QTY_ISS_TY, MST_VAL_ISS_TY, STK_QTY, STK_VAL
              FROM COM_MAT_STORES,  (SELECT  COST_MST_ID CMST,
                                     NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_VALUE) ,
                                                                     '20',  DECODE(SUBSTR(COST_VALUE,1,1), '-', COST_VALUE, COST_VALUE*-1),
                                                                     '21',  COST_VALUE)),0) STK_VAL,
                                     NVL(SUM(DECODE(COST_CSY_COSTEL, '23',  ABS(COST_NO_UNITS) ,
                                                                     '20',  DECODE(SUBSTR(COST_NO_UNITS,1,1), '-', COST_NO_UNITS, COST_NO_UNITS*-1),
                                                                     '21',  COST_NO_UNITS)),0) STK_QTY
                                    FROM COM_COSTS WHERE COST_COST_YEAR = 2009
                                    AND ((COST_CSY_COSTEL = '23' AND COST_TRANS_CODE = 'M') OR (COST_CSY_COSTEL IN ('20','21')))
                                    GROUP BY COST_MST_ID)
           WHERE CMST(+) = MST_ID
           AND (NVL(STK_VAL,0) <> MST_VAL_ISS_TY OR NVL(STK_QTY,0) <> MST_QTY_ISS_TY);Here is the explain plan of the update statement
UPDATE STATEMENT     CHOOSE     56     34119     443547                         
UPDATE COMDBA.COM_MAT_STORES                                             
FILTER                                             
TABLE ACCESS(FULL) COMDBA.COM_MAT_STORES     ANALYZED     56     34119     443547                         
SORT(AGGREGATE)               1     37                         
TABLE ACCESS(BY INDEX ROWID) COMDBA.COM_COSTS          1     25     925                         
INDEX(RANGE SCAN) COMDBA.COM_COST_14          2     97476                              
SORT(AGGREGATE)               1     37                         
TABLE ACCESS(BY INDEX ROWID) COMDBA.COM_COSTS          1     25     925                         
INDEX(RANGE SCAN) COMDBA.COM_COST_14          2     97476                              
SORT(AGGREGATE)               1     37                         
TABLE ACCESS(BY INDEX ROWID) COMDBA.COM_COSTS          1     25     925                         
INDEX(RANGE SCAN) COMDBA.COM_COST_14          2     97476                              
SORT(AGGREGATE)               1     37                         
TABLE ACCESS(BY INDEX ROWID) COMDBA.COM_COSTS          1     25     925                         
INDEX(RANGE SCAN) COMDBA.COM_COST_14          2     97476                              

Answer 1

As a first step you can remove the unwanted sub queries.
update com_mat_stores
   set (
        mst_qty_iss_ty,
        mst_val_iss_ty
       ) = 
            select nvl(sum(decode(cost_csy_costel, '23',  abs(cost_no_units),
                                       '20',  decode(substr(cost_no_units,1,1), '-', cost_no_units, cost_no_units*-1),
                                '21',  cost_no_units)),0) stk_qty,
            nvl(sum(decode(cost_csy_costel, '23',  abs(cost_value) ,
                                '20',  decode(substr(cost_value,1,1), '-', cost_value, cost_value*-1),
                                '21',  cost_value)),0) stk_val                                                              
       from com_costs
      where cost_cost_year = 2009
        and cost_mst_id = mst_id
        and (
             (cost_csy_costel = '23' and cost_trans_code = 'm')
           or
          (cost_csy_costel in ('20','21'))
where (mst_qty_iss_ty, mst_val_iss_ty) !=
               select nvl(sum(decode(cost_csy_costel, '23',  abs(cost_no_units) ,
                                                               '20',  decode(substr(cost_no_units,1,1), '-', cost_no_units, cost_no_units*-1),
                                                               '21',  cost_no_units)),0) stk_qty,
                      nvl(sum(decode(cost_csy_costel, '23',  abs(cost_value) ,
                                                          '20',  decode(substr(cost_value,1,1), '-', cost_value, cost_value*-1),
                                                          '21',  cost_value)),0) stk_val                                                              
                          from com_costs
                         where cost_cost_year = 2009
                           and cost_mst_id = mst_id
                           and (
                                (cost_csy_costel = '23' and cost_trans_code = 'm')
                                 or
                                (cost_csy_costel in ('20','21'))
                         )