SQL (Custom) Unique Constraint for a set of rows

Question

How to create a ( may be custom) unique constraint for a particular no.of rows.

I have table data as below

I want my itemFK column to be Unique for same productionsessionKey value. ie for all yellow (101) itemFK should be Unique and for all blue (102) itemFK should be unique . Else they can be duplicate.

Answer 1

Add a unique constraint on a tupple for those 2 columns

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ALTER TABLE your_table
  ADD CONSTRAINT UC_Your_Table_ProdSession_Item UNIQUE (productionsessionKey, itemFK);