NonStop SQL/MP Reference Manual

NonStop SQL/MP Reference Manual—142115
E-18
Considerations—EXPLAIN
Access path Identifies the path used for retrieving rows from the base table. The
path can be a primary path (the base table) or an alternate path (an
index defined on the base table).
The phrase path forced indicates that the path was specified by the
user with a CONTROL TABLE directive.
Access path also states whether the table is partitioned and whether
access is sequential and pages are kept in cache as long as possible
(called sequential cache). If multiple indexes are scanned (because of
OR'ed predicates in the WHERE clause), then more than one access
path may be shown
Access type Specifies the unit of locking (record or table) and the access method
that controls lock requests (STABLE, REPEATABLE, or BROWSE).
Accessed via view Specifies the fully qualified Guardian name for a protection view
whose underlying table is specified in the report line beginning with
“Table.” For a shorthand view, the view definition becomes part of
the query so that the query plan describes operations on the
underlying tables or views.
Base table pred. Shows the predicates evaluated on the base table and indicates that
evaluation is performed by the disk process.
Begin key pred. Specifies the predicates used to position to the first row to scan,
including collations explicitly (but not implicitly) used in the
predicates.
Characteristic Describes special characteristics of the step, such as whether it
executes once before the operation or once per row retrieved. For
joins, indicates which previous step produced the rows to be joined.
Column processing Indicates the number of columns to be retrieved and the total number
of columns in the tables or views from which they are retrieved.
DP2 aggr. Indicates that aggregate functions are evaluated by DP2.
End key pred. Specifies the predicates used to position to the last row to scan,
including collations explicitly used in the predicates.
Executor aggr. Indicates that aggregate functions are evaluated by the executor and
shows whether they are derived from the first row returned by the
scan or computed for each group.
Executor pred. Shows predicates evaluated by the executor and describes when they
are evaluated:
•
On rows retrieved by the scan
•
On rows after sorting
•
On null augmented rows
•
From the HAVING clause