16.20 - DESCRIBE - Teradata Database - Teradata Vantage NewSQL Engine

Teradata Vantageā„¢ Time Series Tables and Operations

Product
Teradata Database
Teradata Vantage NewSQL Engine
Release Number
16.20
Published
March 2019
Content Type
Programming Reference
Publication ID
B035-1208-162K
Language
English (United States)
Last Update
2019-05-02

Purpose

Expands the SELECT list with aggregates of value_expression over time. DESCRIBE includes both fully parallel and single-threaded (when using VERBOSE) functions.

To invoke the time series version of this function, use the GROUP BY TIME clause. For more information, see GROUP BY TIME Clause.

Syntax



Syntax Elements

VERBOSE
Includes both fully parallel and single-threaded functions.
ALL
All non-null value_expressions, including duplicates, in the computation.
DISTINCT
Excludes duplicates specified by value_expression from the computation.
value_expression
A literal or column expression for which a set of aggregate functions are computed for the series.

The value_expression cannot be a reference to a view column derived from a function, and cannot contain any ordered analytical or aggregate functions.

Return Value

The return value is defined by each aggregate function that is actually invoked.

Nulls are not included in the result computation.

DISTINCT is not used with MODE when DESCRIBE VERBOSE is expanded.

The following functions are included in the result set of DESCRIBE:
  • MAX
  • MIN
  • AVERAGE
  • STDDEV_SAMP
If using the optional VERBOSE keyword, the list of aggregates also includes:
  • MEDIAN
  • MODE
  • 25th PERCENTILE
  • 50th PERCENTILE
  • 75th PERCENTILE

Additional aggregates included with VERBOSE are single-threaded, and require longer processing times. PERCENTILE computations use a linear process to determine if the percentile lies between two data points. VERBOSE includes MODE, which returns duplicate rows with different values.

The HAVING clause references any aggregates included as part of the DESCRIBE function.

Usage Notes

DESCRIBE has the following restrictions:
  • It can only be used in the SELECT list.
  • It cannot be used in comparisons.
  • It cannot be aliased.
  • It cannot be used as an argument to a function.

value_expression must be a numeric data type.