BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  VIEWs are not updated correctly after altering underlying ta          BorlandTalk.com Forum Index -> Delphi Databases (SQL Servers) View previous topic :: View next topic   Author Message Richard Cox Guest Posted: Sun Oct 24, 2004 12:04 am    Post subject: VIEWs are not updated correctly after altering underlying ta I have a view which depends on three tables. The select statement in the view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... and so on. If I add a new field to table A and then perform a SELECT on the view, I see data values shifted one column to the right or left, so that, for example, peoples names end up in the date of birth column. I fix the problem by issuing an ALTER VIEW statement for the view (i.e. a statement which doesn't modify the view at all, just restates its definition), but this seems rather weak. Do I really have to monitor the effect of every change I make to the structure of the database and issue ALTER VIEW statements to "refresh" then? Or is there some nifty command somewhere ("File | Refresh Views"? ) which will do this for me? Many thanks, Richard Cox. Back to top Richard Cox Guest Posted: Sun Oct 24, 2004 12:07 am    Post subject: Re: VIEWs are not updated correctly after altering underlyin ....oops, sorry, forgot to say that I am using MS SQL Server 2000. <blush> Back to top Richard Cox Guest Posted: Tue Aug 23, 2005 8:16 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin Ah...this question was either: a) too stupid to be worth a response, or b) the answer is so fiendishly complex that noone can formulate it, or possibly c) I phrased it badly and noone can understand it. Would someone take pity on me and let me know which? Many thanks, Richard Cox richard underscore cox at traqs dot com "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote Quote: I have a view which depends on three tables. The select statement in the view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... and so on. If I add a new field to table A and then perform a SELECT on the view, I see data values shifted one column to the right or left, so that, for example, peoples names end up in the date of birth column. I fix the problem by issuing an ALTER VIEW statement for the view (i.e. a statement which doesn't modify the view at all, just restates its definition), but this seems rather weak. Do I really have to monitor the effect of every change I make to the structure of the database and issue ALTER VIEW statements to "refresh" then? Or is there some nifty command somewhere ("File | Refresh Views"? ) which will do this for me? Many thanks, Richard Cox. Back to top Kevin Frevert Guest Posted: Tue Aug 23, 2005 9:10 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote Quote: Ah...this question was either: a) too stupid to be worth a response, or No such thing as a stupid question. Quote: b) the answer is so fiendishly complex that noone can formulate it, or possibly Possible. Quote: c) I phrased it badly and noone can understand it. Would someone take pity on me and let me know which? d) Not enough info What databatase are you using? How does this issue relate to Delphi? If your using MSSQL, you should never have to go back and 'refresh' a view if one of the underlying table's structure changes. Oracle or Interbase, someone else will need to jump in. Good luck, krf Quote: "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote in message news:417af182 (AT) newsgroups (DOT) borland.com... I have a view which depends on three tables. The select statement in the view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... and so on. If I add a new field to table A and then perform a SELECT on the view, I see data values shifted one column to the right or left, so that, for example, peoples names end up in the date of birth column. I fix the problem by issuing an ALTER VIEW statement for the view (i.e. a statement which doesn't modify the view at all, just restates its definition), but this seems rather weak. Do I really have to monitor the effect of every change I make to the structure of the database and issue ALTER VIEW statements to "refresh" then? Or is there some nifty command somewhere ("File | Refresh Views"? ) which will do this for me? Back to top Richard Cox Guest Posted: Tue Aug 23, 2005 10:33 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin Thanks for your reply Kevin. Quote: What databatase are you using? I am talking about MS SQL 2000 - I replied to my own message giving that information, having realised my original message missed it out. Quote: How does this issue relate to Delphi? I infer that you think I should be asking this question elsewhere. The question is only related to Delphi insofar as I was using Delphi at the time I experienced the problem. I'll take the question to microsoft.public.sqlserver.server. Richard Cox. "Kevin Frevert" <kevin (AT) workdrinkingdietcoke (DOT) com> wrote Quote: "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote in message news:430b83f5$1 (AT) newsgroups (DOT) borland.com... Ah...this question was either: a) too stupid to be worth a response, or No such thing as a stupid question. b) the answer is so fiendishly complex that noone can formulate it, or possibly Possible. c) I phrased it badly and noone can understand it. Would someone take pity on me and let me know which? d) Not enough info What databatase are you using? How does this issue relate to Delphi? If your using MSSQL, you should never have to go back and 'refresh' a view if one of the underlying table's structure changes. Oracle or Interbase, someone else will need to jump in. Good luck, krf "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote in message news:417af182 (AT) newsgroups (DOT) borland.com... I have a view which depends on three tables. The select statement in the view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... and so on. If I add a new field to table A and then perform a SELECT on the view, I see data values shifted one column to the right or left, so that, for example, peoples names end up in the date of birth column. I fix the problem by issuing an ALTER VIEW statement for the view (i.e. a statement which doesn't modify the view at all, just restates its definition), but this seems rather weak. Do I really have to monitor the effect of every change I make to the structure of the database and issue ALTER VIEW statements to "refresh" then? Or is there some nifty command somewhere ("File | Refresh Views"? ) which will do this for me? Back to top Martin Brekhof Guest Posted: Wed Aug 24, 2005 4:40 am    Post subject: Re: VIEWs are not updated correctly after altering underlyin "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote Quote: Ah...this question was either: view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... I guess you should replace A.* with the exact fieldnames you need (which is better pratice anyway). hth, Martin Back to top Kevin Frevert Guest Posted: Wed Aug 24, 2005 1:45 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote Quote: Thanks for your reply Kevin. What databatase are you using? I am talking about MS SQL 2000 - I replied to my own message giving that information, having realised my original message missed it out. Using Enterprise Manager to manage my views, I've never had to refresh anything to make new fields appear, but in views I rarely issue a 'Select A.*...'. Microsoft's newsgroups would be a good place to start or check out..http://www.fulltextsearch.com and search on views, caching, and execution plan (not sure the best way to enter the keywords). If this is a problem, you cannot be the first one to run into it. Good luck, krf Back to top Richard Cox Guest Posted: Wed Aug 24, 2005 3:50 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin Whilst in process of creating a very detailed message for one of MS newgroups, the cause of the problem dawned on me and I found a number of references on the web - the cause of the problem is, as you say, using "Select * from...". When the underlying tables change, the view goes with the old metadata and still expects to find the columns at the original ordinal position. If they have been rearranged, the data will simply be wrong. (If you delete a field from the underlying table, the view becomes unusable.) Generating a script for all views, sprocs and functions using Enterpise Manager and running it should set everything right. Though I will, of course, stop using "Select * from..." at once! Many thanks for taking an interest. Richard. "Kevin Frevert" <kevin (AT) workdrinkingdietcoke (DOT) com> wrote Quote: "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote in message news:430ba441 (AT) newsgroups (DOT) borland.com... Thanks for your reply Kevin. What databatase are you using? I am talking about MS SQL 2000 - I replied to my own message giving that information, having realised my original message missed it out. Using Enterprise Manager to manage my views, I've never had to refresh anything to make new fields appear, but in views I rarely issue a 'Select A.*...'. Microsoft's newsgroups would be a good place to start or check out..http://www.fulltextsearch.com and search on views, caching, and execution plan (not sure the best way to enter the keywords). If this is a problem, you cannot be the first one to run into it. Good luck, krf Back to top Richard Cox Guest Posted: Wed Aug 24, 2005 4:06 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin Yes, as you will see from my reply to Kevin, that was the cause. Thanks. I wonder why it is considered better practice. Is it because DBMS's don't handle it well, or because there is something more fundamentally wrong with the practice? Should someone write (or has someone written) the article "Create View ... as Select * From ... Considered Harmful"? Richard. "Martin Brekhof" <martin (AT) brekhof (DOT) nl> wrote Quote: "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote in message news:430b83f5$1 (AT) newsgroups (DOT) borland.com... Ah...this question was either: view definition is something like SELECT A.*, B.Name, C.StartDate FROM A Assignment INNER JOIN B.BusinessUnit ON... I guess you should replace A.* with the exact fieldnames you need (which is better pratice anyway). hth, Martin Back to top Richard Cox Guest Posted: Wed Aug 24, 2005 4:13 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin Thanks, Brian. I see that my subject line wording was misleading, since the question was not about views being updated, but rather the view definitions. Richard. "Brian Bushay TeamB" <BBushay (AT) Nmpls (DOT) com> wrote Quote: a) too stupid to be worth a response, or b) the answer is so fiendishly complex that noone can formulate it, or possibly c) I phrased it badly and noone can understand it. Would someone take pity on me and let me know which? It is a very badly worded question. Views in SQL server 2000 are updateable under some circumstances but I am not sure that addresses your question. -- Brian Bushay (TeamB) [email]Bbushay (AT) NMPLS (DOT) com[/email] Back to top Martin Brekhof Guest Posted: Thu Aug 25, 2005 5:35 am    Post subject: Re: VIEWs are not updated correctly after altering underlyin Quote: I wonder why it is considered better practice. Several issues come to mind: - performance (select fieldname1, .. from a etc.) requires less parsing - consistency: a view is a way to present data without requiring updates to (for example) reports if the underlying database structure changes. Example: a view presenting a person's data (surname, last name, address etc.) can hide the fact that because of a developper or dba's decision the table the view originally used has been split, moved, renamed etc. - security/need to know: if not everyone needs to see/update all columns in a table you can create one or more views with a limited exposure of the contained data. hth, Martin Back to top Walter Prins Guest Posted: Sat Aug 27, 2005 8:37 pm    Post subject: Re: VIEWs are not updated correctly after altering underlyin "Richard Cox" <rpcox (AT) traqs (DOT) com> wrote Quote: Yes, as you will see from my reply to Kevin, that was the cause. Thanks. I wonder why it is considered better practice. Is it because DBMS's don't handle it well, or because there is something more fundamentally wrong with the practice? Should someone write (or has someone written) the article "Create View ... as Select * From ... Considered Harmful"? Your experience is actually one example of sorts of why it's considered better. In general in queries you also don't want to use select * from ... for more or less the same reason -- select * is vulnerable to changes to the underlying table. I.e. if you add fields to a table against which you execute select *, you'll get a different number of fields back. This may break code that expects the original number of fields/layout. More or less the same thing applies to view definitions on SQL server it seems, as you've found out... 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