15.00 - Number of Null Rows - Teradata Database

Teradata Database Design

Product
Teradata Database
Release Number
15.00
Content Type
User Guide
Publication ID
B035-1094-015K
Language
English (United States)

Number of Null Rows

This value reports the number of rows having a null primary index.

 

FOR this type of primary index …

The value for this measure is …

unique

better as it approaches 0 and usually, but not necessarily, worse as it gets larger.

non‑unique

A very large number reflects a spike in the distribution, indicating the likelihood of serious problems with an uneven consumption of disk space because all rows with a null primary index hash to the same AMP (see “Number of Distinct Values” on page 422 for a description of the problem).

If the number of rows with null primary indexes columns is significantly larger than 0, then the column set is not a good candidate for a primary index. See Chapter 13: “Designing for Missing Information,” for a description of the many problems nulls cause for database management and suggestions about how to minimize or eliminate nulls from your tables.