About Joining Fragmented Data

Fragmented data is data for a single entity that is split between multiple tables.

For example, a data source might store sales data for customers with last names beginning with the letter A through M in one table and last names from N through Z in another table. With fragmented tables, you need to define all of the join conditions between each fragment and all the related tables. The figure shows the physical joins with a fragmented sales table and a fragmented customer table where the data are fragmented the same way (A through M and N through Z).

Description of the illustration frag_table_ex_v.png

You could have a fragmented fact table and a fragmented dimension table with fragments across different values. You create the joins to the fragmented table and define a one-to-many join, as shown in the Customer A to F and from Customer G to Z to Sales A to M example.

Description of the illustration joins_frag_table.png

Note:

Avoid adding join conditions where they aren't necessary, for example, between Sales A to M and Customer N to Z. Extra join conditions can cause performance degradations.