Constraint in SQL

Constraints:-

1. Primary Key Constraint
2. Unique Key Constraint
3. Foreign Key Constraint


CREATE  TABLE TblEmpDetailsPKey
(
    EmpId        varchar(100),
    EmpName        nvarchar(100),
    Address        char(300),
    City        varchar(30),
    CONSTRAINT CN_PKEY PRIMARY KEY(EmpId)   
)
GO


CREATE  TABLE TblEmpDetailsPKey1
(
    EmpId        varchar(100),
    EmpName        nvarchar(100),
    Address        char(300),
    City        varchar(30),
    PRIMARY KEY(EmpId)   
)
GO

ALTER TABLE TblEmpDetailsPKey DROP Constraint CN_PKEY
GO

-------------------------------------------------------
CREATE TABLE TblEmpDetailsUNKey
(
    EmpId        varchar(100),
    EmpName        nvarchar(100),
    Address        char(300),
    City        varchar(30),
    CONSTRAINT    UN_PKEY UNIQUE(EmpId)   
)
GO

------------------------------------------------------------

--Foreign Key Constraint :-

CREATE TABLE TblEmpDetFKey
(
    EmpId        varchar(100) CONSTRAINT CN_FKEY foreign key references TblEmpDetailsPKey,
    Attendance    int,
    Year        int,
    Percentage    numeric(10,2)   
)
GO
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