SQL CONSTRAINT

CHECK CONSTRAINT

• The CHECK CONSTRAINT specifies a condition on each row in a table.
• EXAMPLE:-

CREATE TABLE Review(

ID int NOT NULL,

Name varchar(50),

Age int,

CHECK (Age>=18));

ERROR

RESULT

DEFAULT CONSTRAINT

• THE DEFAULT CONSTRAINT used to provide a default value to the column.
• EXAMPLE:-

CREATE TABLE Review1(

ID int NOT NULL,

Name varchar(50),

Age int,

City varchar(50) DEFAULT ‘KOLHAPUR’);

RESULT

NOT NULL CONSTRAINT

• NOT NULL CONSTRAINT can not accept NULL values.
• EXAMPLE:-

CREATE TABLE Review2 (

ID int NOT NULL,

Name varchar(50) NOT NULL,

Age int );

ERROR

RESULT

UNIQUE CONSTRAINT

• The UNIQUE CONSTRAINT ensures that all value in the column is different.
• EXAMPLE:-

CREATE TABLE Review3 (

ID int NOT NULL UNIQUE,

Name varchar(50) NOT NULL,

Phone numeric(18, 0) NOT NULL UNIQUE,

Age int);

ERROR

RESULT

PRIMARY KEY CONSTRAINT

• The PRIMARY KEY CONSTRAINT uniquely identifies each record in a table.
• EXAMPLE:-

CREATE TABLE Review4 (

ID int NOT NULL,

Name varchar(50) NOT NULL,

Age int,

PRIMARY KEY (ID) );

ERROR

RESULT

FOREIGN KEY CONSTRAINT

• A FOREIGN KEY CONSTRAINT used to link two tables together.
• EXAMPLE:-

CREATE TABLE Review5 (

OrderID int NOT NULL,

OrderNumber int NOT NULL,

ID int,

PRIMARY KEY (OrderID),

FOREIGN KEY (ID) REFERENCES Review4(ID));

REVIEW 4 TABLE

REVIEW 5 TABLE

SELECT [Name],[Age],[OrderNumber]

FROM [dbo].[Review4]

JOIN [dbo].[Review5]

ON [dbo].[Review4].[ID]= [dbo].[Review5].[ID]

RESULT

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