SQL/MP Query Guide

Analyzing Query Performance
HP NonStop SQL/MP Query Guide—524488-003
6-69
EXPLAIN Plan for UNION Operation
Example 6-41. EXPLAIN Plan for UNION Operation (page 1 of 2)
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Query plan 1
SQL request : Union of Selects
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Plan step 1 : perform a Union
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Operation 1.0 : Union of plan step 2 and plan step 3
Operation 1.1 : Sort
Requested : Explicitly in the query
Sort rows in the : Result of a Union
Purpose : To discard duplicate rows for a Distinct
Sort technique : FASTSORT
Sort type : Plan to use User Process Sort
UPS workspace : 24 Kbytes
Sort key columns : ORDONE.A asc
Sort cost : 1
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Plan step 2
Characteristic : Executes once before plan step 1
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Operation 2.0 : Scan
Table : \SQL1.$DATA7.REG1.ORD1
with correlation name ORDONE
Access type : Record locks, stable access
Lock mode : Chosen by the system
Column processing : Requires retrieval of 1 out of 2 columns
Access path 1 : Primary
SBB for reads : Virtual
Begin key pred. : None
End key pred. : None
Index selectivity : Expect to examine 100% of rows from table
Index pred. : None
Base table pred. : None
Executor pred. : None
Table selectivity : Expect to select 100% of rows from table
Expected row count: 3 rows after the scan
Operation cost : 1
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Plan step 3
Characteristic : Executes once before plan step 1
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Operation 3.0 : Scan
Table : \SQL1.$DATA7.REG1.ORD2
with correlation name ORDTWO
Access type : Record locks, stable access
Lock mode : Chosen by the system
Column processing : Requires retrieval of 1 out of 2 columns
Access path 1 : Primary
SBB for reads : Virtual
Begin key pred. : None
End key pred. : None
Index selectivity : Expect to examine 100% of rows from table
Index pred. : None
Base table pred. : None