This would...

I don't...

Can you wrap the entire job in a TRY CATCH blocks?

In the try block begin and commit the transaction

In the catch block rollback and re-throw the error.

SQL Server caches the execution plan of queries, it may recompile a query a different way if it is executed at different times.

If there is any difference in the text...

CREATE VIEW [dbo].[vwstudent]
AS
SELECT STD.ID,
       STD.StudentId, 
       CASE WHEN STD.EfDate <= c.value THEN DATEADD(MONTH, -2, STD.EfDate)
...

That seems a very odd requirement. Are you sure your users really know what they want?

If you are using SQL 2008 you can't use LEAD and LAG. I think you might be able to use the windowed SUM function though.

;WITH Data AS
(
...

CREATE PROCEDURE #TestDW 
(
    @CheckDayOfWeek bit = 0
) AS
IF @CheckDayOfWeek = 0 OR DATEPART(dw,GETDATE()) IN (3,6) BEGIN
    PRINT 'Hello'
  ...

UPDATE a
   SET a.invalid = 1
  FROM aaaMyTable a
 WHERE EXISTS(SELECT * 
           ...

After rebuilding a clustered index you might also need to rebuild all the non-clustered...

This is equivalent SQL to yours, but instead of checking the left join column in the WHERE to be NULL or equal to something else, you might as well check...

;WITH x AS
(
SELECT * 
  FROM (VALUES ('Flat 1','25 My Street',''),
               ('33...

Where you have:

Convert(CHAR(4),row_number() over (partition by Reg_Type order by PolicyRef@))

replace it with:

RIGHT('0000'+Convert(VARCHAR(4),row_number() over (partition by Reg_Type order by PolicyRef@)),4)

If the OP runs the query...

If the OP runs the query I provided...