Database Reference
In-Depth Information
filtered sample card. (index LOC_CITY_IX): 1
orig. card. : 23
block cnt. table stat. : 5
block cnt. for sampling: 5
max. sample block cnt. : 4294967295
sample block cnt. : 5
min. sel. est. : 0.01000000
index LOC_CITY_IX selectivity est.: 0.04347826
Join Orders
This section depicts all the join orders the CBO has scrutinized. There are n ! ( n factorial) join
orders for an n- way join. Thus, a 5-way join has 120 join orders and a 6-way join has 720. For
higher order joins, it would be a waste of CPU resources to try all possible join orders. Hence,
the CBO does not consider them all and stops examining join orders that exceed the cost of the
best plan found so far.
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OPTIMIZER STATISTICS AND COMPUTATIONS
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GENERAL PLANS
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Considering cardinality-based initial join order.
***********************
Join order[1]: LOCATIONS[L]#0 JOBS[J]#1 DEPARTMENTS[D]#2
EMPLOYEES[EMP]#3 EMPLOYEES[MGR]#4
***************
Now joining: JOBS[J]#1
***************
NL Join
Outer table: Card: 1.00 Cost: 2.00 Resp: 2.00 Degree: 1 Bytes: 48
Inner table: JOBS Alias: J
Access Path: TableScan
NL Join: Cost: 5.02 Resp: 5.02 Degree: 0
Cost_io: 5.00 Cost_cpu: 53510
Resp_io: 5.00 Resp_cpu: 53510
Best NL cost: 5.02
resc: 5.02 resc_io: 5.00 resc_cpu: 53510
resp: 5.02 resp_io: 5.00 resp_cpu: 53510
Join Card: 19.00 = outer (1.00) * inner (19.00) * sel (1)
Join Card - Rounded: 19 Computed: 19.00
Best:: JoinMethod: NestedLoop
Cost: 5.02 Degree: 1 Resp: 5.02 Card: 19.00 Bytes: 75
***************
Now joining: DEPARTMENTS[D]#2
***************
 
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