We have covered the overview related to SQL Server Constraint in the blog – SQL Server Constraint in the table

Lets discuss each constraint in Detail

SQL Server NOT NULL Constraint

The SQL Server NOT NULL Constraint is applied on the Column level in the table. It depicts that the particular column where NOT NULL is applied, that column CANNOT have the NULL values.

Whenever a record is being inserted or updated in the table, this specific column should have the value always.

In some cases when we do not get value in the record, we can impose DEFAULT value also to ensure that record is always inserted with the value.

SQL Server UNIQUE Constraint

As the name suggest UNIQUE constraint applied on the Table Column ensures that all values stored in the column with Constraint UNIQUE have different values.

Creating the UNIQUE Constraint on Table Creation by specifying at column level

CREATE TABLE oracleappshelpUsers
(
    UserId				INT 				NOT NULL UNIQUE,
    GivenName 			VARCHAR(128) 		NOT NULL,
    MiddelName 			VARCHAR(10),
    FamilyName 			VARCHAR(128) 		NOT NULL
);

Creating the UNIQUE Constraint on Table Creation by adding CONSTRAINT as part of Table

CREATE TABLE oracleappshelpUsers
(
    UserId				 INT 				NOT NULL ,
    GivenName 			VARCHAR(128) 		NOT NULL,
    MiddelName 			VARCHAR(10),
    FamilyName 			VARCHAR(128) 		NOT NULL,
	CONSTRAINT UC_Users UNIQUE (UserId,GivenName)
);

SQL Server DROP Constraint

The below SQL Query allows to DROP the applied constraint on the table

ALTER TABLE oracleappshelpUsers
DROP INDEX UC_Users;