今天同事給了兩個SQL，超級大，一個表8000多萬，一個表7800萬，原語句如下：

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update CHANNEL_CHENGDU.o_user_CONS partition(p201011) A
SET unuser_flag = (SELECT unuser_flag
FROM CHANNEL_CHENGDU.o_user partition(p201011) B
WHERE A.SERV_ID = B.SERV_ID)
where EXISTS (SELECT 1
FROM CHANNEL_CHENGDU.o_user partition(p201011) B
WHERE A.SERV_ID = B.SERV_ID);

update CHANNEL_CHENGDU.o_user_CONS partition(p201011) A
SET BILL_USER_FLAG = (SELECT BILL_USER_FLAG
FROM CHANNEL_CHENGDU.o_user partition(p201011) B
WHERE A.SERV_ID = B.SERV_ID)
where EXISTS (SELECT 1
FROM CHANNEL_CHENGDU.o_user partition(p201011) B
WHERE A.SERV_ID = B.SERV_ID);

這兩條語句在執行第一條的時候執行了6個小時沒出結果，就被殺掉了，光回滾就用了2個小時，當時開發人員急於要結果，於是我用以前看到的一篇帖子中提到的方法（

-----執行了889秒
declare
maxrows number default 5000;
row_id_table dbms_sql.Urowid_Table;
p_id_table dbms_sql.Number_Table;
cursor acnt_first_cur is
SELECT /* use_hash(A,B) parallel(A 4) parallel(B 4) */
b.unuser_flag, b.rowid row_id
FROM CHANNEL_CHENGDU.o_user partition(p201011) B,
CHANNEL_CHENGDU.o_user_CONS partition(p201011) A
WHERE A.SERV_ID = B.SERV_ID
and EXISTS (SELECT /*+use_hash(C,D) parallel(C 4) parallel(D 4)*/
1
FROM CHANNEL_CHENGDU.o_user partition(p201011) C,
CHANNEL_CHENGDU.o_user_CONS partition(p201011) D
WHERE C.SERV_ID = D.SERV_ID)
order by b.rowid;
begin
open acnt_first_cur;
loop
exit when acnt_first_cur%notfound;
fetch acnt_first_cur bulk collect
into p_id_table, row_id_table limit maxrows;
forall i in 1 .. row_id_table.count
update CHANNEL_CHENGDU.o_user_CONS partition(p201011)
set unuser_flag = p_id_table(i)
where rowid = row_id_table(i);
commit;
end loop;
end;
/

-----708秒
declare
maxrows number default 5000;
row_id_table dbms_sql.Urowid_Table;
p_id_table dbms_sql.Number_Table;
cursor acnt_first_cur is
SELECT /* use_hash(A,B) parallel(A 4) parallel(B 4) */
b.BILL_USER_FLAG, b.rowid row_id
FROM CHANNEL_CHENGDU.o_user partition(p201011) B,
CHANNEL_CHENGDU.o_user_CONS partition(p201011) A
WHERE A.SERV_ID = B.SERV_ID
and EXISTS (SELECT /*+use_hash(C,D) parallel(C 4) parallel(D 4)*/
1
FROM CHANNEL_CHENGDU.o_user partition(p201011) C,
CHANNEL_CHENGDU.o_user_CONS partition(p201011) D
WHERE C.SERV_ID = D.SERV_ID)
order by b.rowid;
begin
open acnt_first_cur;
loop
exit when acnt_first_cur%notfound;
fetch acnt_first_cur bulk collect
into p_id_table, row_id_table limit maxrows;
forall i in 1 .. row_id_table.count
update CHANNEL_CHENGDU.o_user_CONS partition(p201011)
set BILL_USER_FLAG = p_id_table(i)
where rowid = row_id_table(i);
commit;
end loop;
end;
/