- A junk dimension is used to combine small, low-cardinality attributes into one dimension table.
- In projects, we often have flags like is_active, is_returned, payment_status, order_channel.
- Instead of creating separate dimensions for each, we group them into one junk dimension.
- Each unique combination becomes one row with a surrogate key.
- For example, in a sales fact table, I combined 6–7 yes/no and status fields into a junk dimension.
- This reduced clutter in the fact table and avoided multiple small joins.
- It also improved model clarity in a star schema.
- We typically use junk dimension when attributes are unrelated but frequently used together in reporting.
What is junk dimension?
Updated on February 23, 2026
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