Update a view doesn't work

Question

I'm working on a view which is then updated by the user. This update basically changes the value of column. But right now it doesnt let me do that and produces this :

Update or insert of view or function '' failed because it contains a derived or constant field.

I know this is because I have a constant in the select statement but is there a way to get around it? Please help

This is my code for the view

Create view Schema.View1
as
SELECT
Convert(Varchar(20),l.jtpName) as JobType, Convert(Varchar(10),' <All> ')as SubCategory , Convert(varchar (3), Case when a.jtpName= l.jtpName and a.subName= ' <All> ' then 'Yes' else 'No' end) As AutoProcess from Schema.JobType l left join Schema.Table1 a on l.jtpName=a.jtpName
UNION
SELECT
Convert(Varchar(20),a.jtpName) as JobType, Convert(Varchar(10),a.subName) as SubCategory, Convert(varchar (3),Case when b.jtpName= a.jtpName and b.subName= a.subName then 'Yes' else 'No' end) As AutoProcess from Schema.SubCategory a left join fds.Table1 b on a.subName=b.subName

GO

Finally the update statement:

UPDATE Schema.View1 SET AUTOPROCESS = Case WHEN AUTOPROCESS = 'Yes' Then 'No' END Where JOBTYPE = 'Transport' and SUBCATEGORY= 'Cargo'

Thank You

Answer 1

You cannot update a column that is the result of a computation.

According to MSDN, one of the conditions for a view column to be updatable is this:

• Any modifications, including UPDATE, INSERT, and DELETE statements, must reference columns from only one base table.
• The columns being modified in the view must directly reference the underlying data in the table columns. The columns cannot be derived in any other way, such as through the following:
  • An aggregate function: AVG, COUNT, SUM, MIN, MAX, GROUPING, STDEV, STDEVP, VAR, and VARP.
  • A computation. The column cannot be computed from an expression that uses other columns. Columns that are formed by using the set operators UNION, UNION ALL, CROSSJOIN, EXCEPT, and INTERSECT amount to a computation and are also not updatable.
• The columns being modified are not affected by GROUP BY, HAVING, or DISTINCT clauses.
• TOP is not used anywhere in the select_statement of the view together with the WITH CHECK OPTION clause.

Here not only does your view uses the UNION statement, the AutoProcess field you are trying to update is actually the result of a CASE statement that uses two fields. It makes no sense to try and update that.

I would recommend that you use stored proc to perform writing operations. Or, as Damien suggest, you could use an INSTEAD OF trigger on the view too.