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Considerations
•
"Case Considerations" (page 105)
•
"Number Considerations" (page 105)
•
"Formatted [OPTIONS 'f'] Considerations" (page 105)
•
"Normal User [OPTIONS 'n'] Considerations" (page 106)
•
"Expert User [OPTIONS 'e'] Considerations" (page 108)
•
"Machine-Readable [OPTIONS 'm'] Considerations" (page 110)
Case Considerations
In most cases, words in the commands can be in uppercase or lowercase. The options letter must
be single quoted and in lowercase.
Number Considerations
Costs are given in a generic unit of effort. They show relative costs of an operation.
When numbers are displayed as 0.01 for OPTIONS 'n' (or 0.0001 for OPTIONS 'e'), the numbers
have likely been rounded up and are usually much smaller than shown. However, if the numbers
are zero, the display shows "0".
When trailing decimal digits are zero, they are dropped. For example, 6.4200 would display as
6.42 and 5.0 would display as 5, without a decimal point.
Formatted [OPTIONS 'f'] Considerations
The formatted option is the simplest option. It provides essential, brief information about the
plan and shows the operators and their order within the query execution plan.
OPTIONS 'f' formats the EXPLAIN output into these fields:
LC
RC
OP
OPERATOR
OPT
DESCRIPTION
CARD
This example uses OPTIONS 'f':
>>explain options 'f' select * from region;
LC
RC
OP
---
---
---
3
.
4
2
.
3
1
.
2
.
.
1
--- SQL operation complete.
To use the EXPLAIN statement with a prepared statement, first prepare the query. Then use the
EXPLAIN statement:
Left child sequence number
Right child sequence number
The sequence number of the operator in the query plan
The operator type
Query optimizations that were applied
Additional information about the operator
Estimated number of rows returned by the plan. CARDINALITY and
ROWS_OUT are the same.
OPERATOR
--------------------
root
split_top
partition_access
file_scan
OPT
DESCRIPTION
--------
--------------------
1:64(hash2)
fs fr
REGION
CARD
---------
5.00E+000
5.00E+000
5.00E+000
5.00E+000
EXPLAIN Statement
105
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