Rows With Null in Join Key Missing From Join

KNOWLEDGE BASE

Rows With Null in Join Key Missing From Join

Published: 03 Jul 2018
Last Modified Date: 06 Jul 2018

Issue

Rows with a 'null' value in the join key are excluded from the join and considered mismatched values even if there is a 'null' in the join key for each table.

Environment

Tableau Prep 2018.1

Resolution

As a workaround, replace any join key field containing nulls with a calculated field using one of the functions for null handling in Tableau.

If the join key is a string:

IFNULL([join key], '')

will replace null values with empty strings.

If the join key is a number:

ZN([join key])

will replace null values with zeroes.

Cause

In a relational database, a null is not a value, a null is the absence of a value.
Because of this, two nulls are not treated as logically equivalent, and null join key values are ignored.