Comparing Window Aggregate Functions and Teradata-Specific Functions

Teradata Vantageā„¢ SQL Functions, Expressions, and Predicates

brand
Software
Teradata Vantage
prodname
Teradata Database
Teradata Vantage NewSQL Engine
vrm_release
16.20
category
Programming Reference
featnum
B035-1145-162K

Avoid using Teradata-specific functions such as MAVG, CSUM, and MSUM for applications intended to be ANSI-compliant and portable.

ANSI Function Teradata Function Relationship
AVG MAVG The form of the AVG window function that specifies an aggregation group of ROWS value PRECEDING is the ANSI equivalent of the MAVG Teradata-specific function.

Note that the ROWS value PRECEDING phrase specifies the number of rows preceding the current row that are used, together with the current row, to compute the moving average. The total number of rows in the aggregation group is value + 1. For the MAVG function, the total number of rows in the aggregation group is the value of width.

For AVG window function, an aggregation group of ROWS 5 PRECEDING, for example, means that the 5 rows preceding the current row, plus the current row, are used to compute the moving average. Thus the moving average for the 6th row of a partition would have considered row 6, plus rows 5, 4, 3, 2, and 1 (that is, 6 rows in all).

For the MAVG function, a width of 5 means that the current row, plus 4 preceding rows, are used to compute the moving average. The moving average for the 6th row would have considered row 6, plus rows 4, 5, 3, and 2 (that is, 5 rows in all).

SUM CSUM

MSUM

Be sure to use the ANSI-compliant SUM window function for any new applications you develop. Avoid using CSUM and MSUM for applications intended to be ANSI-compliant and portable.
The following defines the relationship between the SUM window function and the CSUM and MSUM Teradata-specific functions, respectively:
  • The SUM window function that uses the ORDER BY clause and specifies ROWS UNBOUNDED PRECEDING is the ANSI equivalent of CSUM.
  • The SUM window function that uses the ORDER BY clause and specifies ROWS value PRECEDING is the ANSI equivalent of MSUM.

    Note that the ROWS value PRECEDING phrase specifies the number of rows preceding the current row that are used, together with the current row, to compute the moving average. The total number of rows in the aggregation group is value + 1. For the MSUM function, the total number of rows in the aggregation group is the value of width.

    Thus for the SUM window function that computes a moving sum, an aggregation group of ROWS 5 PRECEDING means that the 5 rows preceding the current row, plus the current row, are used to compute the moving sum. The moving sum for the 6th row of a partition, for example, would have considered row 6, plus rows 5, 4, 3, 2, and 1 (that is, 6 rows in all).

    For the MSUM function, a width of 5 means that the current row, plus 4 preceding rows, are used to compute the moving sum. The moving sum for the 6th row, for example, would have considered row 6, plus rows 5, 4, 3, and 2 (that is, 5 rows in all).

    Moreover, for data having fewer than width rows, MSUM computes the sum using all the preceding rows. MSUM returns the current sum rather than nulls when the number of rows in the sample is fewer than width.