The Teradata optimizer has always had options available to it when performing SQL. It always attempts to use the most efficient path to provide the answer set. This is true for aggregation as well.
When performing aggregation, the main shortcut available might include the use of a secondary index. The index row is maintained in a subtable. This row contains the row ID (row hash + uniqueness value) and the actual data value stored in the data row.
Therefore, an index row is normally much shorter than a data row. Hence, more index rows exist in an index block than in a data block.
As a result, the read of an index block makes more values available than the actual data block. Since I/O is the slowest operation on all computer systems, less I/O equates to faster processing. If the optimizer can obtain all the values it needs for processing by using the secondary index, it will. This is referred to as a "covered query."
The creation of a secondary index is covered in this book as part of the Data Definition Language (DDL).
Teradata Related Interview Questions
|Microstrategy Interview Questions||Informatica Interview Questions|
|MySQL Interview Questions||Oracle 11g Interview Questions|
|Hadoop Interview Questions||TeraData DBA Interview Questions|
|MYSQL DBA Interview Questions||Database Administration Interview Questions|
|DB2 SQL Programming Interview Questions||Hadoop Administration Interview Questions|
|Java Hadoop Developer Interview Questions||Informatica MDM Interview Questions|
|Informatica Admin Interview Questions||Hadoop Testing Interview Questions|
Teradata Related Practice Tests
|Microstrategy Practice Tests||Informatica Practice Tests|
|MySQL Practice Tests||Oracle 11g Practice Tests|
|Hadoop Practice Tests||TeraData DBA Practice Tests|
|MYSQL DBA Practice Tests||Database Administration Practice Tests|
|DB2 SQL Programming Practice Tests||Hadoop Administration Practice Tests|
Teradata Parallel Architecture
Fundamental Sql Using Select
On-line Help And Show Commands
Date And Time Processing
Character String Processing
Reporting Totals And Subtotals
Data Definition Language
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