We are developing a database that consolidates few SQL Server DBs for a reporting requirement. Each DB has a number of views. No direct table or SP objects require to be accessible. All DBs and the new DB sitting in the same server. So we can develop cross-database queries quite easily with the Fully qualified object names.
i.e SELECT * FROM [SERVER].[DATABASE].[Schema].[View]
The problem is the depending database names differ between dev/ staging/ production environments of depending databases.
We have investigated the Synonym approach for the individual views and working fine. The advice we trying to seek from someone expert here is what is the best practice we should adhere to creating a single point to maintain this database alias instead of creating synonyms for each view so that we could do this once per environment and can maintain new queries same across different environments.
SQL Server and Oracle terminology -
In SQL Server If I have two applications and want to keep the database completely separate, I could simply create 1 database for each application therefore I end up with 2 databases.
If I wanted to do the same thing in oracle, what do I need to create?
- create a new "Databases"? "Instance", "Schema", or "Tablespace" per application?
(Note, these two applications is the same application used by two different companies, that do not share data!)
Reference: http://www.codeproject.com/Tips/492342/Concept-mapping-between-SQL-Server-and-Oracle
Having worked with SQL Server a lot in the past, I have sympathy with trying to figure out how Oracle organizes things as I struggled with the same thing. My comments below are from SQL Server 2000 and 2003 so forgive me if things have changed since then.
Previous responders have been helpful. I think one problematic assumption here is that there is an exact "level" equivalency between SQL Server and Oracle. What I mean by "level" is something that occupies the same space in the hierarchies that you have diagrammed above (and which, btw, I think are a good place to start but might need a bit of editing in a couple of places, for example how you have diagrammed "user" and "schema" in the Oracle hierarchy, I might put them side-by-side.) I do not think these concept "levels" match exactly between the DB platforms.
A schema in Oracle is somewhat equivalent to a separate database in SQL Server but not entirely.
I would say that the "walls" -- not an exact technical term but oh well -- between databases in SQL server are a bit higher than the "walls" between schemas in Oracle. Others might disagree but here is my reasoning:
a. A schema in Oracle is a purely logical construct. It denotes who has ownership of objects. It has nothing to do with the physical location or layout of the objects. A tablespace (orthagonal concept, as noted by a previous poster) indicates the physical location of objects. A tablespace can hold objects that are in multiple schemas and vice versa. In SQL Server these two concepts are sort of merged into one -- a database is both tablespace and schema, more or less, although in some respects within a DB in SQL Server you then have multiple owners with various object ownership. This can get a bit confusing because as I remember (it's been a couple of years) if not using NT Authentication the users are defined at the server level and then have to "link" to the users in the individual DBs.
b. I remember finding it easier, or at least a bit simpler, to assure myself that users to two separate DBs in SQL Server had no access to the relative other user's DB than I have found it in Oracle.
c. Because a DB in SQL server represents both physical storage and logical ownership, you can detach the DB and move it to another SQL Server Instance and attach it. You can't do this with a schema in Oracle. I mean, you can datapump the data out or back it up or whatever to another server and another schema, but that all takes at least some scripting and such or at least a fair amount of clicking in Enterprise Manager. It doesn't give you the one-click "Detach DB" option that you have in SQL Server which makes it a lot easier to get the idea that SQL Server DBs are units that you can more-or-less move back and forth between databases.
To sum things up, I think either option would work. That is, 1) Create two separate instances of Oracle with one schema in each instance for each application, or 2) Create two separate schemas in one Oracle instance.
There are pros and cons for each option. Option 1 is probably going to be more work to set up and configure but will also give you more separation, independence, ability to have separate hardware, etc., for each DB. Option 2 will be quite a bit simpler but gives you less separation between the data and greater risk of configuration screw-ups or other things allowing users of one schema to access the other. It also means you have to be a bit more careful that someone writing a query accessing data in one schema doesn't use all the CPU and IO resources and starve a user on the other schema.
Also, yes, you could use pluggable databases in 12c. However, given the fact that you need to ask these questions (no shame, just pointing out where you're at) makes me hesitant about recommending what can easily be a more complex setup.
TL;DR -- SQL Server isn't Oracle and Oracle isn't SQL Server. Either option works and there are pros and cons to each.
If you're using 12.1 or later with the multitenant option, you could create separate pluggable databases in a single container database. The other option, which works in any version of Oracle, would be to create a separate schema. It would be possible, as well, to create a separate database, though that is generally not the preferred approach unless you have a particular need to do things like upgrade the database that one application is using without affecting the other.
Creating a Database
If you create a separate database, you'd end up with complete separate memory structures (i.e. the SGA and PGA for each database would be separate) as well as a completely separate set of background processes (each database would have its own log writer process(es) for example). That is a very heavyweight option-- you can't have too many databases on a single server before you start having a lot of contention for RAM, for scheduling all the background processes, etc. It does provide for the maximum separation between different applications-- each database can be running a different version of Oracle with a different set of initialization parameters-- but this also tends to increase the complexity of managing the environment. This generally only makes sense when you have third party applications that require a specific version of the database or a specific set of initialization parameters.
Creating a Schema
If you create a separate schema, you still have a single database so the two schemas are sharing the same memory structures (competing with each other for space in the SGA's buffer cache, for example), initialization parameters, etc. You have to exercise a modicum of planning to ensure that that the two don't interfere with each other-- you'd probably want to make sure that nether application creates public synonyms or at least that they won't wan to create the same public synonym as the other application-- but this is generally pretty trivial.
Creating a Pluggable Database
This only works in 12.1 and only if you have the multitenant option. This is the most similar to the SQL Server concept of creating a new database for each application.
You should create a new instance (schema) on the same database, where the schema in oracle is the same as the SQL server database
I've currently got a "Web" edition SQL Azure server with on database on it. I want to put another database on there but am unsure how the costing works. Will I need to pay the £9.99 per database or database server?
Does it make more sense just to set up a couple of different schemas in my existing database to try and reduce costs?
You pay per database. Creating schemas may make sense if cost is your concern. I have seen this done multiple times. However keep in mind that a few SQL Server/Azure features are schema independent. For example user-defined statistics and roles are schema independent. So as long as you don't use these features you should be good with a schema-based separation.
I am not a DBA and so dont really know anything about SQL 2005 security settings, etc. I am attempting to set up an empty copy of our database by generating the full database from SQL Management Studio generated scripts. Unfortunately I don't know what many of the options do and the MSFT documentation of this processes isn't great.
There is an option to generate script for Schemas, Tables, Views and Users. It is the users I am confused about, because I don't understand how they affect the usage of the database. We have some developers in the team who are in this list and some who are not, yet everyone can do anything on the database, at least when they are hosting it on their own machines.
Do I need to keep these Users in my new generated database and what do they do?
We also have a dbo User who is a db_owner and owns many of our schemas. What is this dbo User? What is the significance of a user Owning Schemas? We use Schemas as "namespaces" to group logically related tables in our database but I take it there is more to them than that?
There is also a username tied to this dbo User, its the windows NT login of one of our developers, but he doesn't have his own User object in the list...is there any significance to this? Is this a bad thing?
Other Users are guest, INFORMATION_SCHEMA and sys, but I think these are all defaults?
Sorry but I am a SQL admin ignoramus and usually left these things to the DBA in my previous job!
Thanks for any help.
Do I need to keep these Users in my new generated database and what do they do
The answer is it depends. If your applications use a mixed mode authentication then you will need the user accounts created in SQL. If you use windows authentication (and it sounds like you are) then you might not need them.
What is the significance of a user Owning Schemas?
In SQL Server 2005 all schemas must be owned by a user. Schemas can be used to group functionality but they can also be used to group security. For example a user account may only have access to a specific schema (or multiple schemas).
Hopefully that helps answer some of your questions
I'm no beginner to using SQL databases, and in particular SQL Server. However, I've been primarily a SQL 2000 guy and I've always been confused by schemas in 2005+. Yes, I know the basic definition of a schema, but what are they really used for in a typical SQL Server deployment?
I've always just used the default schema. Why would I want to create specialized schemas? Why would I assign any of the built-in schemas?
EDIT: To clarify, I guess I'm looking for the benefits of schemas. If you're only going to use it as a security scheme, it seems like database roles already filled that.. er.. um.. role. And using it a as a namespace specifier seems to have been something you could have done with ownership (dbo versus user, etc..).
I guess what I'm getting at is, what do Schemas do that you couldn't do with owners and roles? What are their specifc benefits?
Schemas logically group tables, procedures, views together. All employee-related objects in the employee schema, etc.
You can also give permissions to just one schema, so that users can only see the schema they have access to and nothing else.
Just like Namespace of C# codes.
They can also provide a kind of naming collision protection for plugin data. For example, the new Change Data Capture feature in SQL Server 2008 puts the tables it uses in a separate cdc schema. This way, they don't have to worry about a naming conflict between a CDC table and a real table used in the database, and for that matter can deliberately shadow the names of the real tables.
I know it's an old thread, but I just looked into schemas myself and think the following could be another good candidate for schema usage:
In a Datawarehouse, with data coming from different sources, you can use a different schema for each source, and then e.g. control access based on the schemas. Also avoids the possible naming collisions between the various source, as another poster replied above.
If you keep your schema discrete then you can scale an application by deploying a given schema to a new DB server. (This assumes you have an application or system which is big enough to have distinct functionality).
An example, consider a system that performs logging. All logging tables and SPs are in the [logging] schema. Logging is a good example because it is rare (if ever) that other functionality in the system would overlap (that is join to) objects in the logging schema.
A hint for using this technique -- have a different connection string for each schema in your application / system. Then you deploy the schema elements to a new server and change your connection string when you need to scale.
At an ORACLE shop I worked at for many years, schemas were used to encapsulate procedures (and packages) that applied to different front-end applications. A different 'API' schema for each application often made sense as the use cases, users, and system requirements were quite different. For example, one 'API' schema was for a development/configuration application only to be used by developers. Another 'API' schema was for accessing the client data via views and procedures (searches). Another 'API' schema encapsulated code that was used for synchronizing development/configuration and client data with an application that had it's own database. Some of these 'API' schemas, under the covers, would still share common procedures and functions with eachother (via other 'COMMON' schemas) where it made sense.
I will say that not having a schema is probably not the end of the world, though it can be very helpful. Really, it is the lack of packages in SQL Server that really creates problems in my mind... but that is a different topic.
I tend to agree with Brent on this one... see this discussion here. http://www.brentozar.com/archive/2010/05/why-use-schemas/
In short... schemas aren't terribly useful except for very specific use cases. Makes things messy. Do not use them if you can help it. And try to obey the K(eep) I(t) S(imple) S(tupid) rule.
I don't see the benefit in aliasing out users tied to Schemas. Here is why....
Most people connect their user accounts to databases via roles initially, As soon as you assign a user to either the sysadmin, or the database role db_owner, in any form, that account is either aliased to the "dbo" user account, or has full permissions on a database. Once that occurs, no matter how you assign yourself to a scheme beyond your default schema (which has the same name as your user account), those dbo rights are assigned to those object you create under your user and schema. Its kinda pointless.....and just a namespace and confuses true ownership on those objects. Its poor design if you ask me....whomever designed it.
What they should have done is created "Groups", and thrown out schemas and role and just allow you to tier groups of groups in any combination you like, then at each tier tell the system if permissions are inherited, denied, or overwritten with custom ones. This would have been so much more intuitive and allowed DBA's to better control who the real owners are on those objects. Right now its implied in most cases the dbo default SQL Server user has those rights....not the user.
I think schemas are like a lot of new features (whether to SQL Server or any other software tool). You need to carefully evaluate whether the benefit of adding it to your development kit offsets the loss of simplicity in design and implementation.
It looks to me like schemas are roughly equivalent to optional namespaces. If you're in a situation where object names are colliding and the granularity of permissions is not fine enough, here's a tool. (I'd be inclined to say there might be design issues that should be dealt with at a more fundamental level first.)
The problem can be that, if it's there, some developers will start casually using it for short-term benefit; and once it's in there it can become kudzu.
In SQL Server 2000, objects created were linked to that particular user, like if a user, say
Sam creates an object, say, Employees, that table would appear like: Sam.Employees. What
about if Sam is leaving the compnay or moves to so other business area. As soon you delete
the user Sam, what would happen to Sam.Employees table? Probably, you would have to change
the ownership first from Sam.Employees to dbo.Employess. Schema provides a solution to
overcome this problem. Sam can create all his object within a schemam such as Emp_Schema.
Now, if he creates an object Employees within Emp_Schema then the object would be
referred to as Emp_Schema.Employees. Even if the user account Sam needs to be deleted, the
schema would not be affected.
development - each of our devs get their own schema as a sandbox to play in.
Here a good implementation example of using schemas with SQL Server. We had several ms-access applications. We wanted to convert those to a ASP.NET App portal. Every ms-access application is written as an App for that portal. Every ms-access application has its own database tables. Some of those are related, we put those in the common dbo schema of SQL Server. The rest gets its own schemas. That way if we want to know what tables belong to an App on the ASP.NET app portal that can easily be navigated, visualised and maintained.