sql - null value in foreign key -


i copied following paragraph http://msdn.microsoft.com/en-us/library/ms175464(v=sql.105).aspx

a foreign key constraint can contain null values; however, if column of composite foreign key constraint contains null values, verification of values make foreign key constraint skipped. make sure values of composite foreign key constraint verified, specify not null on participating columns.

could provide me simple example me understand above? verification foreign key constraint do? think has referential integrity.

thanks lot.

you shouldn't need example if think of in way.

if any of fields in composite foreign key null none of other fields checked integrity until all fields of key provided.


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