CONSTRAINTS PROVIDE A MECHANISM PROVIDE INTEGRITY IN THE DATABASE.THERE ARE THREE TYPES OF CONSTRAINTS IN SQL SERVER.
TO CREATE A TABLE BEFORE WE HAVE TO CHECK CONDITION.THERE ARE THREE TYPES OF CONSTRAINT IN SQL SERVER
1) DOMAIN INTEGRITY CONSTRAINT.
2 ENTITY INTEGRITY CONSTRAINT.
3) REFERENTIAL INTEGRITY CONSTRAINT.
DOMAIN INTEGRITY CONSTRAINT: 1) NOT NULL
2) CHECK
NOT NULL: CREATE TABLE EMP(EMPID INT CONSTRAINT PK_EMPID NOT NULL,EMPNAME VARCHAR(90))
CHECK:
CREATE TABLE EMP(EMPID CONSTRAINT PK_EMPID CHECK (EMPID<100))
ENTITY INTEGRITY CONSTRAINT: 1) PRIMARY KEY CONSTRAINT
2) UNIQUE KEY CONSTRAINT
PRIMARY KEY: PRIMARY KEY RESTRICT DUPLICATE VALUES AND NULL VALUES
CREATE TABLE EMP(EMPID INT CONSTRAINT PK_EMPID PRIMARY KEY(EMPID), EMPNAME VARCHAR(90))
UNIQUE KEY: UNIQUE KEY RESTRICT DUPLICATE VALUES AND ALLOW ONE NULL VALUES
CREATE TABLE EMP(EMPID INT CONSTRAINT PK_EMPID UNIQUE(EMPID), EMPNAME VARCHAR(90))
REFERENTIAL INTEGRITY CONSTRAINT: PARENT TABLE CHILD TABLE RELATIONSHIP
PARENT TABLE: CREATE TABLE EMP(EMPID INT CONSTRAINT PK_EMPID PRIMARY KEY(EMPID),EMPNAMEE VARCHAR(90))
CHILD TABLE
CREATE TABLE EMPLIST(EMPID INT REFERENCES EMP(EMPID),EMPSALARY MONEY)
REGARDS