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;