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Newbie Question Re: Stored Procedures/Views

Posted on 1998-08-06
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Last Modified: 2010-03-19
Here is my situation: I am using several views to consolidate data from a rather large table. The selection criteria is based on the contents of another table (that holds the names of the fields to be shown in the views.)

When a user makes a change to the selection criteria through my VB app, the selection criteria tables will be changed. This is a "trigger" to drop and recreate the existing views.  

Since I can't drop/create views in triggers or stored procedures, I was wondering if there is a way to call a VB exe from a stored procedure? Or if there is some better way to drop and create a view when a non-related table changes. I know I can do it through the program itself, but I would much prefer do it directly through sql to keep the views in sync with the selection criteria table.
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Question by:trillian30
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by:mitek
ID: 1089431
I don't think you can create a view from an SQL Server trigger. The way I would approach this problem, would be creating an SQL stored procedure that would (using dynamic SQL, of course) drop and re-create the view, based on parameters passed to it.
This procedure would be called from VB app whenever "a user makes a change to the selection criteria"

Yes, there IS a way to call an external program from SP (xp_cmdshell) but I wouldn't even dare to use it to call anything larger than 'dir' command.

I would think, the way to do that is not "to call a VB exe from a stored procedure", but just the other way around. This way, it would be a simple call to SP, which would dynamicly build a DROP/CREATE VIEW statement and handle everything cleanly.

Again, can't give you an ANSWER, but a general plan of actions.

Tell me what you think about it.

BTW, that's NOT a newbie question.

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by:mitek
ID: 1089432
A really sick way of going about this problem would be to write a batch script for isql utility, that would drop/create the views, and call this file via xp_cmdshell from a trigger.
But only a sick (or really geniuos) mind could design something like THAT ...


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by:trillian30
ID: 1089433
My understanding is that you also can not create a View in a stored procedure.  I'm not really sure what you mean by 'dynamic sql' though.
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Expert Comment

by:mitek
ID: 1089434
I didn't say so. You CAN create a view from an SP, but it looks like it's not possible to call this SP from an SQL Server TRIGGER -- that's one of inherent limitations of triggers in SQL Server.

as for dynamic sql ? it's when you make a query within a stored procedure and then execute it with EXECUTE() command.

like that:

  DECLARE @01 varchar(255),@02 varchar(255),@03 varchar(255),@04 varchar(255)

  SELECT @01 = 'DROP VIEW testView '
  SELECT @02 = 'CREATE VIEW testView AS '
  SELECT @03 = 'SELECT * FROM ForumTopics '
  SELECT @04 = 'WHERE TopicSecurity=''MEM'''
  EXECUTE (@01)             -- drop the view
  EXECUTE (@02 + @03 + @04) -- recreate the view


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by:trillian30
ID: 1089435
You are *so* fabulous! That worked perfectly! Do you want to resubmit so you can get the points for the answer?

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mitek earned 800 total points
ID: 1089436
Yep. Thank you very much. Let me know if you still have problems with it.

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