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Sql can a foreign key be null

sql can a foreign key be null

to: create table whatever (someid.
But if you can make it simple, why make it complex?
Instead of inserting/updating one row in one table, you need to access four rows in four different tables.Which makes it more difficult for the programmer to understand and use, Please!Don't do it, it's terrible.Creating columns is cheap.This model establishes a one-to-one relationship between the parent and foreign keys that allows undetermined values (nulls) in the foreign key.The reason it can have zero is because orders were imported from a legacy order system where customer details where not held.Jams, sep 27 wtm copy protection crack serial '11 at 18:07 From the horse's mouth: Foreign keys allow key values that are all null, even if there are no matching primary or unique keys No Constraints on the Foreign Key When no other constraints are defined on the foreign.So your proposal table would gta 5 cheats xbox 360 slidey cars have two foreign keys, one with the client npav crack serial key ID and one with the sales rep.Most commonly a sendout applies as long as the information is there, in which case both fromdate and enddate are null.Making queries becomes this mess of, "if it's type 1, join to this table, otherwise join to this".Can you explain why?
Well, if we want access the information to display in the maintenance form for sendouts, the most natural would be to have one select, and join the two subtables with left join.
Because the logical information is scattered over four tables, which makes it more difficult for the programmer to understand and use, and makes it more difficult in support situations to view the data.
Many with one single column beside the primary key.Null by definition is not a value.So you have an order table and the order details table for instance.Answered Dec 19 '14 at 15:46 zeeEclipse I think foreign key of one table also primary key to some other it won't allows there is no question of having null value in foreign key.Edited Mar 22 at 19:59 answered Aug 4 '15 at 15:41 anopres 1, If the salesperson is null, it means that one has not been assigned."Don't know if one has been assigned" is a nonsense interpretation, and your solution is a confusing hack that surprisingly pretends that "unassigned" is somehow a person.