我有一个过程，其中使用其他表的列上的sum和nvl函数填充表的列。这些更新查询速度很慢，这会使整体Proc速度变慢。此类更新查询之一如下：
UPDATE t_final wp
SET PCT =
(
SELECT SUM(NVL(pct,0))
FROM t_overall
WHERE rid = 9
AND rtype = 1
AND sid = 'r12'
AND pid = 21
AND mid = wp.mid
)
WHERE rid = 9 AND rtype = 1 AND sid = 'r12' AND pid = 21;
这里t_overall和t_final，两个表都没有任何索引，因为它们在整个过程中都有多个更新。表t_final的记录数约为8500，表t_overall的记录数约为13000。还有其他方法，我可以以更优化的方式编写上述查询吗？
编辑1：此处SUM（NVL（pct，0））函数首先将表t_overall的'pct'列中的null替换为0，然后使用sum函数将所有pct值相加，并根据更新表t_final的pct列条件。
解释计划返回如下：
OPERATION OBJECT_NAME CARDINALITY COST
UPDATE STATEMENT 6 424
UPDATE T_FINAL
TABLE ACCESS(FULL) T_FINAL 6 238
. Filter Predicates
. AND
. RTYPE=6
. SID='R12'
. RID=9
. PID=21
SORT(AGGREGATE) 1
TABLE ACCESS(FULL) T_OVERALL 1 30
Filter Predicates
AND
MID-:B1
RTYPE=6
SID='R12'
RID=9
PID=21
更新的行数约为2200
编辑2：我已经使用提示/ * + collect_plan_statistics * /运行更新查询，如下所示：
ALTER session SET statistics_level=ALL;
UPDATE /*+ gather_plan_statistics */ t_final wp
SET PCT =
(
SELECT SUM(NVL(pct,0))
FROM t_overall
WHERE rid = 9
AND rtype = 1
AND sid = 'r12'
AND pid = 21
AND mid = wp.mid
)
WHERE rid = 9 AND rtype = 1 AND sid = 'r12' AND pid = 21;
select * from
table (dbms_xplan.display_cursor (format=>'ALLSTATS LAST'));
结果是：
SQL_ID gypnfv5nzurb0, child number 1
-------------------------------------
select child_number from v$sql where sql_id = :1 order by
child_number
Plan hash value: 4252345203
---------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | OMem | 1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2 |00:00:00.01 | | | |
| 1 | SORT ORDER BY | | 1 | 1 | 2 |00:00:00.01 | 2048 | 2048 | 2048 (0)|
|* 2 | FIXED TABLE FIXED INDEX| X$KGLCURSOR_CHILD (ind:2) | 1 | 1 | 2 |00:00:00.01 | | | |
---------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter(("KGLOBT03"=:1 AND "INST_ID"=USERENV('INSTANCE')))
谢谢。
答案 0 :(得分：0)
您没有提供足够的信息来进行独特的诊断，所以我只能提示您如何对查询进行故障排除。
这是我的设置模拟您的数据
create table t_final as
select rownum mid, 8 + mod(rownum,4) rid, 1 rtype, 'r12' sid, 21 pid, 0 pct from dual
connect by level <= 8800;
drop table T_OVERALL;
create table T_OVERALL as
select mod(rownum,8800) mid, 8 + mod(rownum,4) rid, 1 rtype, 'r12' sid, 21 pid, rownum pct from dual
connect by level <= 13000;
现在，我运行查询以激活统计信息收集以查看查询在做什么：
SQL> UPDATE /*+ gather_plan_statistics */ t_final wp
2 SET PCT =
3 (
4 SELECT SUM(NVL(pct,0))
5 FROM t_overall
6 WHERE rid = 9
7 AND rtype = 1
8 AND sid = 'r12'
9 AND pid = 21
10 AND mid = wp.mid
11 )
12 WHERE rid = 9 AND rtype = 1 AND sid = 'r12' AND pid = 21;
2200 rows updated.
Elapsed: 00:00:00.97
因此，经过了将近一秒钟的时间，如果您进行了大量此类更新，这将很慢。要查看原因，我们显示光标和统计信息（可以使用提示/*+ gather_plan_statistics */来获得历史记录）
SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------------------
SQL_ID 3ctaz5gvksb54, child number 0
-------------------------------------
UPDATE /*+ gather_plan_statistics */ t_final wp SET PCT = (
SELECT SUM(NVL(pct,0)) FROM t_overall WHERE rid
= 9 AND rtype = 1 AND sid = 'r12' AND pid =
21 AND mid = wp.mid ) WHERE rid = 9 AND rtype =
1 AND sid = 'r12' AND pid = 21
Plan hash value: 1255260726
-------------------------------------------------------------------------------------------
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------
| 0 | UPDATE STATEMENT | | 1 | | 0 |00:00:00.96 | 116K|
| 1 | UPDATE | T_FINAL | 1 | | 0 |00:00:00.96 | 116K|
|* 2 | TABLE ACCESS FULL | T_FINAL | 1 | 2200 | 2200 |00:00:00.01 | 33 |
| 3 | SORT AGGREGATE | | 2200 | 1 | 2200 |00:00:00.92 | 112K|
|* 4 | TABLE ACCESS FULL| T_OVERALL | 2200 | 33 | 3250 |00:00:00.85 | 112K|
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------------------
2 - filter(("RID"=9 AND "RTYPE"=1 AND "PID"=21 AND "SID"='r12'))
4 - filter(("RID"=9 AND "RTYPE"=1 AND "PID"=21 AND "MID"=:B1 AND "SID"='r12'))
所以您看到主要问题出在FULL TABLE SCAN上的T_OVERALL上，它被调用了2200次（列开始，第4行）。
一种补救措施可以根据第4行的过滤谓词提供一个索引：
create index T_OVERALL_IDX on T_OVERALL(mid, rid, rtype, sid, pid);
在相同的数据上，我得到了：
Elapsed: 00:00:00.05
更改后的计划现在使用2200 INDEX RANGE SCAN s
---------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------------
| 0 | UPDATE STATEMENT | | 1 | | 0 |00:00:00.05 | 10272 |
| 1 | UPDATE | T_FINAL | 1 | | 0 |00:00:00.05 | 10272 |
|* 2 | TABLE ACCESS FULL | T_FINAL | 1 | 2200 | 2200 |00:00:00.01 | 33 |
| 3 | SORT AGGREGATE | | 2200 | 1 | 2200 |00:00:00.01 | 5755 |
| 4 | TABLE ACCESS BY INDEX ROWID| T_OVERALL | 2200 | 33 | 3250 |00:00:00.01 | 5755 |
|* 5 | INDEX RANGE SCAN | T_OVERALL_IDX | 2200 | 1 | 3250 |00:00:00.01 | 2505 |
---------------------------------------------------------------------------------------------------------
如果您发现其他行为，可以简单地对数据重新检查相同的方法。