I am using oracle database for a web application.
Is there a table inside system database that records any or all changes that occur inside the database?
For example, if I insert a row or update a row, it would record this change inside a table.
Does this kind of table exist inside oracle database?
In mysql there is INFORMATION_SCHEMA TABLES that records everything that occurs inside the database.
Oracle too provides auditing mechanisms for your DB however, the subject is very extensive to be treated in a simple answer, since control can go down to a very fine grained auditing. Take a look at Oracle Documentation on this theme, good luck.
Related
Looks like SQL Server 2008 and later uses the concept of "temporal tables" to manage table data history:
https://learn.microsoft.com/en-us/sql/relational-databases/tables/temporal-table-usage-scenarios
Looks like the following clause is used to accomplish this:
WITH (SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.MyTableHistory));
Let's assume that a data model has tables TableX and a TableXHistory and I select the following context menu path to generate a DDL script of TableX:
Script Table as > CREATE to > New Query Editor Window
If the generated SQL script does not have a text reference to "HISTORY_TABLE" then can I say 100% that the history table is not managed as a temporal table? Also, would a temporal table be explicitly displayed in the standard tables directory for the data model? Is there any reason not to use temporal tables in 2018 as opposed to manually created history tables? My first impression is that anyone who creates manual history tables in 2018 is most likely out of date with SQL Server capabilities.
Temporal tables available only from 2016. Technology is not mature yet.
Temporal tables have their own Pros & Cons. Other options should be considered (classic triggers and history table, change data capture, replication, etc.)
The main disadvantages of temporal tables for me:
multiple changes made at the same time are invisible (only one row is returned)
history tables must be located at the same DB
limitation for transactional replication, merge replication is not supported
issues when system time has been changed - no way to know which update was first w/o implementing additional logic (version)
history tables can'be updated w/o disabling versioning
to get net changes you need to query the base table (which is not good).
how to detect which columns are changed? (CDC & triggers can detect that naturally, with temporal it may be very expensive)
...
. I have two databases in same azure sql server .i want that both database interact to each other using trigger. i.e If any record is inserted in Customer table of first database the trigger gets fired and record is inserted in another database.
We had / have the same problem with triggers that we use for insert-update-delete where we write a record to Database-1 that has the primary table, but also updates Database-2 where we hold "archive" versions of the tables.
The only solution we have identified and are testing is to bring all of the tables into a single database and separate the different tables under separate database schemas in the one database.
Analysis so far of this approach looks promising.
I think what you're trying to do is not allowed in Sql Azure. From my expertise what you are trying to do is a bad practice on-premise as well (think backups-restore and availability issue scenarios).
You should move the dependency in the application and have the application update both databases, as appropriate.
Anyway, if you want to continue with this approach please take a look over Elastic Query feature: https://learn.microsoft.com/en-in/azure/sql-database/sql-database-elastic-query-overview
Please let me know if I can help with something
I’m after a bit of advice on the best way to go about this is SQL server 2008R2 express. I have a number of applications that are in separate databases on the same server. They are all “plugins” that use a central staff/structure list that will be in a separate database. The application is in the process of being migrated from JET.
What I’m looking for is the best way of all the “plugin” databases being able to see the central database and use those tables in standard queries and views etc.
As I’m using express that rules out any replication solution and so far the only option I can think of is to use triggers or a stored procedure to “push” out all the changes to the plugins. The information needs to be populated on a near enough real time basis however the number of changes will be very small maybe up to 100 a day and the biggest table only has about 1000 rows at the moment (the staff names table).
Hopefully that will cover all everything but if anyone needs any more details then just ask
Thanks
Apologies if I've misunderstood, but from your description it sounds like all these databases are hosted on the same instance of SQL Server - it's your mention of replication that makes me uncertain.
Assuming that's the case, you should be able to replace any copies of tables from the central database which are held in the "plugin" databases with views or synonyms which reference the central tables directly, since SQL server allows you to make references between databases on the same server using three-part naming (database_name.schema_name.object_name)
For example, if each plugin db has a table StaffNames, you could replace this with a view by dropping the table, then creating a view:
drop table StaffNames
go
create view StaffNames
as
select * from <centraldbname>.<schema - probably dbo>.StaffNames
go
and your code should continue to work seamlessly, as long as permissions are set up.
Alternatively, you could replace all the references to the shared tables in the plugin databases with three-part name references to the central database, but the view method requires less work.
One thing I want to do is build a personal database for myself at home to use a financial database (transaction log, checking/savings account tables, etc), and I want to do this mainly to learn more about developing databases. I am pretty familiar with MS Access, though not put to use in this context, but what I am really trying to learn is SQL Server.
SO, that being said, the first question that popped into my mind is that if I have a transactions table that I would want to use as a ledger, then is there some method to have the table automatically perform a calculation for one field (balance) based on another field(s) (expense, revenue fields)? Similar to what someone may do with Excel......
Or is this something I would have to do with an unbound form, and an UPDATE statement kinda of approach? If a table constraint exists for this type of idea, I would like to learn it....
I mentioned MS Access in the title, but a SQL Server is also most appreciated. Thanks for the help!
Derived data should not be stored except if it needs to be indexed -- you calculate the values in your SQL statements, or in the presentation layer.
In addition to computed columns in SQL Server tables, you can have them in VIEWS and you can index them. The term is "indexed view" and when you do that, the data is persisted in a hidden temp table and updated on the fly when the data the VIEW is derived from is changed. You can read about it under the TYPES OF VIEWS topic in the same link cited in #Roland Bouman's answer.
Last of all, it's not clear to me why you mention Access at all if you're using SQL Server as your back end. Are you developing your front end in Access?
In MS SQL server, you can use computed columns for this: http://msdn.microsoft.com/en-us/library/ms191250.aspx
We are in the process of a multi-year project where we're building a new system and a new database to eventually replace the old system and database. The users are using the new and old systems as we're changing them.
The problem we keep running into is when an object in one system is dependent on an object in the other system. We've been using views, but have run into a limitation with one of the technologies (Entity Framework) and are considering other options.
The other option we're looking at right now is replication. My boss isn't excited about the extra maintenance that would cause. So, what other options are there for getting dependent data into the database that needs it?
Update:
The technologies we're using are SQL Server 2008 and Entity Framework. Both databases are within the same sql server instance so linked servers shouldn't be necessary.
The limitation we're facing with Entity Framework is we can't seem to create the relationships between the table-based-entities and the view-based-entities. No relationship can exist in the database between a view and a table, as far as I know, so the edmx diagram can't infer it. And I cannot seem to create the relationship manually without getting errors. It thinks all columns in the view are keys.
If I leave it that way I get an error like this for each column in the view:
Association End key property [...] is
not mapped.
If I try to change the "Entity Key" property to false on the columns that are not the key I get this error:
All the key properties of the
EntitySet [...] must be mapped to all
the key properties [...] of table
viewName.
According to this forum post it sounds like a limitation of the Entity Framework.
Update #2
I should also mention the main limitation of the Entity Framework is that it only supports one database at a time. So we need the old data to appear to be in the new database for the Entity Framework to see it. We only need read access of the old system data in the new system.
You can use linked server queries to leave the data where it is, but connect to it from the other db.
Depending on how up-to-date the data in each db needs to be & if one data source can remain read-only you can:
Use the Database Copy Wizard to create an SSIS package
that you can run periodically as a SQL Agent Task
Use snapshot replication
Create a custom BCP in/out process
to get the data to the other db
Use transactional replication, which
can be near-realtime.
If data needs to be read-write in both database then you can use:
transactional replication with
update subscriptions
merge replication
As you go down the list the amount of work involved in maintaining the solution increases. Using linked server queries will work best if its the right fit for what you're trying to achieve.
EDIT: If they're the same server then as suggested by another user you should be able to access the table with servername.databasename.schema.tablename Looks like it's an entity-framework issues & not a db issue.
I don't know about EntityToSql but I know in LinqToSql you can connect to multiple databases/servers in one .dbml if you prefix the tables with:
ServerName.DatabaseName.SchemaName.TableName
MyServer.MyOldDatabase.dbo.Customers
I have been able to click on a table in the .dbml and copy and paste it into the .dbml of the alternate project prefix the name and set up the relationships and it works... like I said this was in LinqToSql, though have not tried it with EntityToSql. I would give it shot before you go though all the work of replication and such.
If Linq-to-Entities cannot cross DB's then Replication or something that emulates it is the only thing that will work.
For performance purposes you probably want either Merge replication or Transactional with queued (not immediate) updating.
Thanks for the responses. We're going to try adding triggers to the old database tables to insert/update/delete records in the new tables of the new database. This way we can continue to use Entity Framework and also do any data transformations we need.
Once the UI functions move over to the new system for a particular feature, we'll remove the table from the old database and add a view to the old database with the same name that points to the new database table for backwards compatibility.
One thing that I realized needs to happen before we can do this is we have to search all our code and sql for ##Identity and replace it with scope_identity() so the triggers don't mess up the Ids in the old system.