SQL Cost Compared To Elapsed Time

I posted this a while back with a lot more text and I don't think it ever posted, perhaps I was hitting some size limit. So here is the really short version. It occurred to me that a good way to find SQL which Oracle may be coming up with the wrong plan for is to compare the cost to the elapsed time. If the elapsed time per unit of cost is much higher than normal then Oracle might be using the wrong plan. The query below was my attempt to locate such SQL. Has anyone ever tried this?

• Tested on 9ir2

col address format a30
col cost format 99990.999
col elap_sec_per_cost format 99990.999

select a.address,

1. cost, round(b.elap_time_per_exe/100000/a.cost ,3) elap_sec_per_cost from
   (select address,sum(cost) cost from v$sql_plan
   where cost is not null group by address) a,
   (select address, decode(executions,0,0,elapsed_time/executions)
   elap_time_per_exe from v$sqlarea) b where a.address=b.address order by 3 desc;

address                              cost elap_sec_per_cost
------------------------------ ---------- -----------------
070000000DDC1EC0                    2.000             0.685
070000000EF6ED50                    5.000             0.118
070000000D9980C0                    4.000             0.105
070000000E487980                    5.000             0.088
070000000FAD18A8                    5.000             0.084
070000000D50ED10                    4.000             0.070

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