Cascading referential integrity constraint

CREATE TABLE [dbo].[tblDepartment](

[depId] [int] NOT NULL,

[depName] [nvarchar](20) NOT NULL

);

CREATE TABLE [dbo].[tblEmployees](

[empId] [int] IDENTITY(1,1) NOT NULL,

[empName] [nvarchar](20) NOT NULL,

[empEmail] [nvarchar](20) NULL,

[empDepId] [int] NULL

);


INSERT [dbo].[tblDepartment] ([depId], [depName]) VALUES (1, 'ECE');

INSERT [dbo].[tblDepartment] ([depId], [depName]) VALUES (2, 'CSE');

INSERT [dbo].[tblDepartment] ([depId], [depName]) VALUES (3, 'IT'); 




INSERT [dbo].[tblEmployees] ([empId], [empName], [empEmail], [empDepId]) VALUES (1, 'datta', 'kumar@g.com', 3);

INSERT [dbo].[tblEmployees] ([empId], [empName], [empEmail], [empDepId]) VALUES (3, 'Teja', 'teja@g.com', 1);

--set default

ALTER TABLE tblEmployees

ADD CONSTRAINT df_DepId

DEFAULT 1 FOR empDepId;


delete from tblDepartment where depId=3;


1. No Action: This is the default behaviour. No Action specifies that if an attempt is made to delete or update a row with a key referenced by foreign keys in existing rows in other tables, an error is raised and the DELETE or UPDATE is rolled back.


2. Cascade: Specifies that if an attempt is made to delete or update a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are also deleted or updated.



3. Set NULL: Specifies that if an attempt is made to delete or update a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are set to NULL.  


4. Set Default: Specifies that if an attempt is made to delete or update a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are set to default values.


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