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Question:  If we have two relation R(A,B,C) and S(D,E,F),where A and D are primary key and attribute C is working as Foreign key and referring to D.So is it possible to C have  NULL in some rows??

Reference:: https://gateoverflow.in/2151/Gate-cse-2012-question-43?state=showcomments-2377&show=2377#a2377

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edited by
https://www.geeksforgeeks.org/constraints-on-relational-database-model/amp/

https://en.m.wikipedia.org/wiki/Referential_integrity

C can take either null values or some value of D. The only restriction is that C should not take any value which is not equal to some row value of D.
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Hii @shishir__roy 

Thanks for reply.can you please share some valid document related to this if you have.

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1 Answer

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Yes it is possible for C have NULL in some rows. Foreign key value can be either NULL or some value from referenced Attribute D.

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