碰到一个想不通的问题，求教大虾！

写了两段Script，感觉做的是同样的事情，但是执行计划的差距惊人的夸张，百思不得其解。
第一段：
 INSERT INTO ODS_TEMP_SHIP_CYCLE_TIME
                SELECT c1.site,
                c1.shift_timekey,
                c1.factory,
                c1.mat_id,
                c1.gls_id,
                c1.lot_id,
                c1.event_timekey,
                c1.hour_timekey,
                c1.oper_code,
                c1.oper_ver,
                c1.plan,
                c1.plan_ver,
                c1.product,
                c1.product_ver,
                c1.flow,
                c1.flow_ver,
                c1.production_type,
                c1.owner_code,
                c1.GROUP_ID,
                c1.mat_state,
                c1.mat_process_state,
                c1.mat_grade,
                c1.mat_judge,
                c1.product_type,
                c1.unit_type,
                c1.user_id,
                c1.eqp_id,
                c1.recipe_id,
                c1.cst_id,
                c1.rework_state,
                c1.logged_in_time,
                c1.logged_out_time,
                c1.arrive_event_name,
                c1.arrive_time,
                c1.arrive_gls_qty,
                c1.arrive_pnl_qty,
                c1.leave_event_name,
                c1.leave_time,
                c1.leave_gls_qty,
                c1.leave_pnl_qty,
                c1.cycle_time,
                c1.main_oper_cycle_time,
                c1.main_oper_process_time,
                c1.main_oper_waiting_time,
                c1.bank_time,
                'N',
                '',
                '',
                sysdate
           FROM eds_cycle_time_mat@etl2edb c1
          WHERE     c1.site = 'C1'
                AND c1.factory = 'CELL'
                AND c1.unit_type = 'Panel'
                AND EXISTS
                       (SELECT 0
                          FROM eds_first_ship_panel@etl2edb f
                         WHERE     1 = 1
                               AND c1.mat_id = f.pnl_id
                               AND c1.factory = f.factory
                               AND c1.site = f.site
                               AND f.shift_timekey >= '20130901 073000'
                               AND f.shift_timekey < '20130902 073000');第二段：
INSERT INTO ODS_TEMP_SHIP_CYCLE_TIME
         SELECT *
           FROM eds_cycle_time_mat@etl2edb c1
          WHERE     c1.site = 'C1'
                AND c1.factory = 'CELL'
                AND c1.unit_type = 'Panel'
                AND EXISTS
                       (SELECT 0
                          FROM eds_first_ship_panel@etl2edb f
                         WHERE     1 = 1
                               AND c1.mat_id = f.pnl_id
                               AND c1.factory = f.factory
                               AND c1.site = f.site
                               AND f.shift_timekey >= '20130901 073000'
                               AND f.shift_timekey < '20130902 073000');
第一段的Plan
INSERT STATEMENT  ALL_ROWSCost: 116,144,469  Bytes: 782  Cardinality: 2  
3 FILTER  
1 REMOTE REMOTE SERIAL_FROM_REMOTE EDS_CYCLE_TIME_MAT ETL2EDBCost: 698,734  Bytes: 751,504,346  Cardinality: 1,922,006  
2 REMOTE REMOTE SERIAL_FROM_REMOTE EDS_FIRST_SHIP_PANEL ETL2EDBCost: 3  Bytes: 75  Cardinality: 1  第二段的Plan
Plan
INSERT STATEMENT  ALL_ROWSCost: 0  
1 REMOTE REMOTE SERIAL_FROM_REMOTE ETL2EDBODS_TEMP_SHIP_CYCLE_TIME和eds_cycle_time_mat表结构是一样的，之所以想写成第一种方式是避免以后eds_cycle_time_mat变更时需要变更第一个表。