Oct 10, 2019
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));
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’);
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 );
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);
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) );
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));
SELECT [Name],[Age],[OrderNumber]
FROM [dbo].[Review4]
JOIN [dbo].[Review5]
ON [dbo].[Review4].[ID]= [dbo].[Review5].[ID]
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