我有一个过程，其中使用其他表列上的 sum 和 nvl 函数填充表的列。这些更新查询很慢，这使得整个 Proc 变慢。这样的更新查询之一如下：
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 ，这两个表都没有任何索引，因为它们在整个过程中有多个更新。表 t_final 的记录数约为 8500，表 t_overall 的记录数约为 13000。还有其他方法吗，我可以用更优化的方式编写上述查询吗？
编辑 1：这里 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 函数添加所有 pct 值，并根据标准更新表 t_final 的 pct 列。
在下面解释计划回报：
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')))
谢谢你。