两列引用另一个表中的单个列

Question

A similar question is asked here multiple foreign keys referencing single column in other table but the syntax is not shown in the answer. I would like to know how this can be accomplished in SQL server. The following syntax gives error

ALTER TABLE ItemIssue ADD CONSTRAINT FK_ItemIssue_Person 
FOREIGN KEY (PersonID, AdvisorID) REFERENCES Person (PersonID)
;

ERROR: Number of referencing columns in foreign key differs from number of referenced columns, table 'ItemIssue'.

--  Create Tables 
CREATE TABLE ItemIssue ( 
ItemIssueID int identity(1,1)  NOT NULL,
PersonID int,
AdvisorID int,
    )
;
CREATE TABLE Person ( 
PersonID int NOT NULL,
Name nvarchar(500),
)

;

Answer 1

You need to define two foreign keys, one for each column:

ALTER TABLE ItemIssue ADD CONSTRAINT FK_ItemIssue_Person 
   FOREIGN KEY (PersonID) REFERENCES Person (PersonID)
;

ALTER TABLE ItemIssue ADD CONSTRAINT FK_ItemAdvisor_Person 
   FOREIGN KEY (AdvisorID) REFERENCES Person (PersonID)
;

Answer 2

It is impossible to create one foreign key for two columns referencing one column. Create them seperate:

ALTER TABLE ItemIssue 
ADD CONSTRAINT FK_ItemIssue_Person_Person FOREIGN KEY (PersonID) REFERENCES Person (PersonID),
ADD CONSTRAINT FK_ItemIssue_Advisor_Person FOREIGN KEY (AdvisorID) REFERENCES Person (PersonID);

Answer 3

To define two foreign keys, one for each column-

Table

Contract - HospidPharmacyId Column

Hospice- HospiceID PK Pharmacy PharmacyId Pk

• Using Following Query we can apply 2 Foreign Key for 1 column.

Alter Table Contract Add Constraint fk_pharmacyID Foreign Key ([HospIDPharmID]) references Pharmacy([PharmacyID])

Alter TAble contract Add Constraint Fk_hospId Foreign key ([HospIDPharmID]) references Hospice(HospiceID)

• In the Contract Table for column-HospidPharmacyId we can insert common value in both the

tables. those which are present in hospice & not in Pharmacy then we cant insert that value in

contract table & vice versa.