Question

EmpID DeptID

1     1
1     2
2     1
3     2
4     5
5     2
1     1   
2     1   

I would like to have a constraint that will make sure that the pair of field is always unique ,such data as last two shown in the example should not be insert-able into the table .in the above table
please note that last two rows are duplicates ,I would like to prevent such data from occuring .
How do I achieve this in sqlserver 2005.Thanks

Answer 1

ALTER TABLE <YourTable, sysname, Emp> 
ADD CONSTRAINT <YourConstraintName, sysname, uix> 
UNIQUE NONCLUSTERED (EmpID,DeptID) 

(Paste into SSMS and use (CTRL + Shift + M))

Or to do this at table creation and as it sounds as though there is no alternative key use.

CREATE TABLE EMPLOYEE_DEPARTMENT(
    EmpID int NOT NULL REFERENCES EMPLOYEE(EmpID),
    DeptID int NOT NULL REFERENCES DEPARTMENT(DeptID),
 CONSTRAINT PK_EMPLOYEE_DEPARTMENT PRIMARY KEY CLUSTERED (EmpID ASC,DeptID ASC)
)