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Teradata RDBMS forUNIX SQL Reference - NCR

NCR Teradata RDBMS forUNIX SQL Reference - NCR, 1997. - 913 p.
Download (direct link): teradataforunix1997.pdf
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By way of the sort key in spool field1...
Fieldl is created to allow a tag sort.
Computed globally...
The computation involves all the intermediate spool file data.
Condition...
An intermediate condition that joins table rows (as compared with the overall join condition).
Duplicated on all AMPs...
A spool file containing intermediate data that is used to produce a result is copied to all AMPs containing data with which the intermediate data is compared.

Teradata RDBMS for UNIX SQL Reference

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Teradata SQL Syntax Guide

EXPLAIN Modifier

Term Explanation
Eliminating duplicate rows...
Duplicate rows can exist in spool files; not in tables. A DISTINCT operation.
END TRANSACTION step..
This indicates that processing is complete and that any locks on the data may be released. Changes made by the transaction are committed.
Estimated size...
This value, based on any statistics collected for a table, is used to estimate the size of the spool file needed to accommodate spooled data. If statistics have not been collected for a table, this estimate may be grossly incorrect (see “COLLECT STATISTICS” statement).
Estimated time...
This approximate time is based on average times for the suboperations that comprise the overall operation, and the likely number of rows involved in the operation. The accuracy of the time estimate is also affected by the accuracy of the estimated size.
Execute the following steps in parallel...
This identifies a set of steps that are processed concurrently. The explanatory text immediately following the list describes the execution of each step.
Join condition...
The overall constraint that governs the join. In the following statement, “Employee.EmpNo = Department.MgrNo” is the overall constraint governing the join. SELECT DeptName, Name FROM Employee, Department WHERE Employee.EmpNo = Department.Mgrno;
Last Use...
This term identifies the last reference to a spool file that contains intermediate data that produces a statement’s final result. The file is released following this step
Locally on the AMPs...
That portion of spooled intermediate or result data for which an AMP is responsible is stored on the AMP; it is not duplicated on or redistributed to other AMPs that are processing the same request.

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Teradata RDBMS for UNIX SQL Reference
Teradata SQL Syntax Guide

EXPLAIN Modifier

Term Explanation
Lock...
The Teradata RDBMS places an Access, Read, Write, or Exclusive lock on a database, table, or row that is to be accessed by a request.
Merge join...
One of the types of join processing performed by the Teradata RDBMS.
Nested join...
One of the types of join processing performed by the Teradata RDBMS
No residual conditions...
Rows are selected in their entirety; there are no specific search conditions. All applicable conditions have been applied to the rows.
Product join...
One of the types of join processing performed by the Teradata RDBMS.
Redistributed by hash code to all AMPs...
Given the values of an indexed or non-indexed column, rows are sent to the AMPs that are responsible for storing the rows that use these values as a primary index.
Single-AMP JOIN step by way of the unique primary index...
A row is selected on a single AMP using the unique primary index for the table. Using a value in the row that hashes to a unique index value in a second table, the first row is joined with a second row located on another AMP.
Single-AMP RETRIEVE by way of unique index # n...
A single row of a table is selected using a unique secondary index value that hashes to the AMP on which the table row is stored.
Single-AMP RETRIEVE step by way of the unique primary index...
A single row of a table is selected using a unique primary index value that hashes to the single AMP on which the data row is stored. Although not explicitly stated in the LOCK portion of the Explain text, a rowhash lock is required because the table is accessed via the unique primary index.

Teradata RDBMS for UNIX SQL Reference

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Teradata SQL Syntax Guide

EXPLAIN Modifier

Term Explanation
SORT to order Spool n by row hash...
Rows in the spool file are sorted by hash code to put them the same order as rows in the primary table, or in another spool file on the same AMP, with which they are to be matched
SORT to order Spool n by row hash and the sort key in spool field1 eliminating duplicate rows...
Rows in the spool file are sorted by hash code using a uniqueness sort to eliminate duplicate rows. Uniqueness is based on the data in field1. The contents of field1 depend on the query and may comprise any of the following: • A concatenation of all the fields in the spool row (used for queries with SELECT DISTINCT or that involve a UNION, INTERSECT, EXCEPT, or MINUS operation). • A concatenation of the row IDs that identify the data rows from which the spool row was formed (used for complex queries involving subqueries). Some other value that uniquely defines the spool row (used for complex queries involving aggregates and subqueries).
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