Using Transaction - sql-server

Question

How do I alter the following procedure in such a way that if insert statement is not successfully executed because of PrimaryKey or something the Delete Statement must also not be executed and further more it should generate an error message that I would Write myself.
CREATE PROCEDURE [dbo].[ReAdmissionInsert]
#GRNo varchar(4),
#ClassId numeric(2),
#FacultyId numeric(1),
#Section varchar(1),
#SessionId numeric(1)
AS
begin
insert into ReAdmissionDtl(GRNo,ClassId,FacultyId,Section,SessionId) values(#GRNo,#ClassId,#FacultyId,#Section,#SessionId)
delete from Discharge where GRNo = #GRNo
end

Answer 1

You use BEGIN TRAN & COMMIT to create a transaction that will be rolled back if your INSERT or DELETE fails:
CREATE PROCEDURE [dbo].[Readmissioninsert] #GRNo VARCHAR(4),
#ClassId NUMERIC(2),
#FacultyId NUMERIC(1),
#Section VARCHAR(1),
#SessionId NUMERIC(1)
AS
BEGIN
BEGIN TRAN --<= Starting point of transaction
INSERT INTO readmissiondtl
(grno,
classid,
facultyid,
section,
sessionid)
VALUES (#GRNo,
#ClassId,
#FacultyId,
#Section,
#SessionId)
DELETE FROM discharge
WHERE grno = #GRNo
COMMIT --<= End point of transaction
END
Documentation
You can use a TRY CATCH for the error message:
How to rollback a transaction in TSQL
TRY CATCH THROW: Error handling changes in T-SQL

Answer 2

Use a transaction and a try catch block. Raise your error in the catch block, like so:
CREATE PROCEDURE [dbo].[ReAdmissionInsert]
#GRNo varchar(4),
#ClassId numeric(2),
#FacultyId numeric(1),
#Section varchar(1),
#SessionId numeric(1)
AS
begin
Begin transaction
Begin try
insert into ReAdmissionDtl(GRNo,ClassId,FacultyId,Section,SessionId)
values(#GRNo,#ClassId,#FacultyId,#Section,#SessionId)
delete from Discharge where GRNo = #GRNo
Commit transaction
End try
Begin catch
Rollback
Raiserror(999999,'my message',16,1)
End catch
end

Answer 3

Best Practice for Writing SQL Server Stored Procedure with Transaction -
Enclose withing TRY..CATCH block
Check for ##TRANCOUNT and ROLLBACK Transaction on ERROR
RAISE actual ERROR to alarm calling program
Sample -
CREATE PROCEDURE [dbo].[ReAdmissionInsert]
#GRNo varchar(4),
#ClassId numeric(2),
#FacultyId numeric(1),
#Section varchar(1),
#SessionId numeric(1)
AS
BEGIN
SET NOCOUNT ON
BEGIN TRY
BEGIN TRAN
insert into ReAdmissionDtl(GRNo,ClassId,FacultyId,Section,SessionId)
values(#GRNo,#ClassId,#FacultyId,#Section,#SessionId)
delete from Discharge where GRNo = #GRNo
COMMIT TRAN
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0
ROLLBACK TRAN
/*ERROR OCCURED*/
DECLARE #ERROR_MESSAGE NVARCHAR(4000);--MESSAGE TEXT
DECLARE #ERROR_SEVERITY INT;--SEVERITY
DECLARE #ERROR_STATE INT;--STATE
SELECT #ERROR_MESSAGE = ERROR_MESSAGE(),
#ERROR_SEVERITY = ERROR_SEVERITY(),
#ERROR_STATE = ERROR_STATE()
/*RETURN ERROR INFORMATION ABOUT THE ORIGINAL ERROR THAT CAUSED
EXECUTION TO JUMP TO THE CATCH BLOCK.*/
RAISERROR (#ERROR_MESSAGE, #ERROR_SEVERITY, #ERROR_STATE)
END CATCH
END
Notice that ##TRANCOUNT is checked to verify if there is any open transactions and ERROR messages are retained and raised so program will receive SqlException.