A foreign key is used to connect two tables.The foreign key in one table references the primary key of the another table( some case it can refer the primary key of the same table also).The table containing the primary key is parent and table containg the foreign key is child table.
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);
First PersonID is the foreign key column in the child table and Persons is the parent table .Persons(PersonID) indicates the primary key of parent table.
eg.CREATE TABLE Order (
Oid int NOT NULL,
Ono int NOT NULL,
PersonID int,
PRIMARY KEY (Oid),
FOREIGN KEY (PersonID) REFERENCES
Persons(PersonID)
);
The value of the foreign key either one of the value present in the parents tables primary column or it can be null.
1. The table being created must have a column named personid
True
2. The create table will fail because 2 tables can not have a field with the named personid
False
3. personid in this table must be unique.
false
foreignkey need not be unique.the only constraint is it must have value that is either present in parent table or it can be null.
4. There must be a different table named persons previously created
True
Since we are creating a link ,the parent table must be present before creating the foreign key references.
If the following appeared in a CREATE TABLE statement FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) true false...
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A foreign key value must exist in the table where it is a primary key. True? False?
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1> Alter Table Department_JCS 2> Add Constraint Department_fk 3> Foreign Key (ManagerSSN) References Employee_JCS(EmployeeSSN) 4> GO Msg 547, Level 16, State 1, Server DESKTOP-54BQ7EN\LOCALDB#743D77CD, Line 1 The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "Department_fk". The conflict occurred in database "master", table "dbo.Employee_JCS", column 'EmployeeSSN'. How can I get rid of this problem and make a foreign key to with the given variables? Am I making a syntax error or is it something else?
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