I am developing a web application (using classic asp for now) that needs to query two tables on two separate databases on the same server.
I have been given separate application-level login/passwords for each database by the IT team which will be used in my code to connect.
I want to create a query that links two tables (one from each database) together, but not too sure how, and Google hasn't helped me much either.
I'm assuming I have to create two connections to do this as I have two separate logins, but how then would I create a query that uses tables from each.
Just a note - our IT team will not at this stage link the two databases together. I'm pretty much stuck with what I have.
Hope you can help.
Mat
If the IT team wants the databases to be separate, you obviously can't use the database to do the join for you.
You'd have to execute the join client side. Linq is an easy way to do that, but a loop with two datasets also works.
The typical syntax for a cross database query would be something like:
SELECT <columns>
FROM [schema].[table] t1 INNER JOIN
[databaseName].[schema].[table] t2 ON <condition>
However, if you're using 2005 or above, it's well worth creating a synonym in the first database so that the reference to the second database isn't peppered throughout your code (what if the database name changes later)?
CREATE SYNONYM [schema].[synonymName] FOR [databaseName].[schema].[table]
Then your query becomes:
SELECT <columns>
FROM [schema].[table] t1 INNER JOIN
[schema].[synonymName] t2 ON <condition>
You may need to set permissions appropriately such that the user you are using to connect to the first database has access to the second. If the IT team simply grants the relevant access to both databases from the same server principal, that is the best way to achieve it. If you are stuck with having two totally separate logins then that sucks. But there isn't any need to 'link the databases together' in order to run a cross-database query.
Related
I am using a SQL database and MS Access 2019 as the front end. The SQL database tables are linked to the Access db using an ODBC connection.
All my queries (they have multiple joined linked tables) run just fine, but as soon as I add a join to a table stored in the Access app (for example, a small table just for mapping values) the query will slow to a crawl. Doesn't matter if the joined fields are indexed or what type of join I'm using.
If anyone has seen this behaviour and found a solution I would much appreciate hearing it.
Joining tables from two separate databases requires the client app to retrieve both tables in their entirety in order to determine the rows needed. That's why it's slow.
If your Access table is small, try using a stored procedure on the SQL side with the data from Access moved to a temporary table. (Or better yet, move the Access table to SQL).
I have a question about how to perform database queries against different database systems?
For example, I have a following SQL query string:
SELECT A.F1, A.F2, B.F3, B.F4
FROM TableA A, TableB B
WHERE A.ID=B.ID AND B.ID=xyz
Is there any solution that I can perform the above query when:
TableA is from an Oracle database, TableB is also from an Oracle database from another instance
TableA is from a SQL Server database, TableB is from an Oracle database
TableA is from an Oracle database, TableB is from a SQL Server database
TableA is from a SQL Server database, TableB is also from a SQL Server database from another SQL Server instance
I know that for situation #1 I can use the ORACLE DATABASE LINK feature (also maybe #3). But is there any common solution which can address all of the scenarios above? For instance, maybe there is another scenario that I want to join two tables from MySQL and SQL Server databases.
For coding I am using C#/.NET, any recommendation is welcome, including joining the data in the code.
Thanks!
This is known as a federated query
You can use SQL Servers federation ability (linked servers) and run the query in SQL Server. You can use Oracles federation ability (Oracle heterogeneous services) and run the query in Oracle.
Either way you need to pick a database server, make the other (foreign) database known to that server then execute the query on the server.
Keep in mind you cannot expect good performance from this as in most cases the executing server is loading all the source records locally and joining locally.
Otherwise you need to write your own 'federation' ability in your app. This is non trivial, i.e. data types don't match exactly between vendors so you need to build some smarts. Also if you are joining particularly large tables you'd better make sure your algorithm is optimised or you'll run our of memory. Further to this, federated query ability in existing products (SQL, Oracle, Cognos etc.) is the result of very large companies doing a lot of development.
Can you tell us how many records you expect to join, and are the various source database servers mostly fixed or is this for an ad hoc query tool?
Is that possible? I'm using Aquadesk and I can't get it to work. The tables have a matching unique identifier and wondering if I can match them up in some way.
What you need - as I think - are "Federated Servers" (Databases) (you can look this up)
The basic idea behind that is, the you can create (catalog) a table in you local Database that is already residing on an other Database (or Server, or even an other DB System, but that depends in you SQL system and version) -> that is defintely a question for your DBAS
You get a table like 'MYSQL'.'PERSONS' that resides remotely (eg. 'BASE','PERSDATA'), so you can use them in a
`SELECT *
from 'LOCALNAME'.'USERS usr
JOIN 'MYSQL'.'PERSONS' pers
on usr.user_id=pers.id`
So jou can select and join over different Databases (and Servers)
I only used that whith IBM/UDB but it works realy fine, and has a fair performance (altough heavily depending on your statement)
I am using ColdFusion 9.1.
I need to use two different datasources in some of my queries. I know it can be done because I see other code that uses two different datasources and it works fine.
I've tried lots of combinations but can't get anything to work, but I know that both of my datasources are working properly.
I have a default database set up in the THIS scope. The default is "DatasourceOne".
<cfquery>
SELECT UserID
FROM DatasourceOne.TableOne IN (SELECT Userid FROM DatasourceTwo.TableTwo )
</cfquery
What are the rules or guidelines about using multiple datasources?
CLARIFICATION
I should have originally asked how I could use two database (not datasources) in a single query. I am sure your answers would have been different. We do have both databases set up as datasources though and I was a little confused myself.
Depending on your database, if the second database is on the same server (or is defined as a linked server) and the user in the datasource has permission, you can usually reference the other database.
SELECT * FROM myTable
WHERE myField IN
(SELECT otherField FROM otherDatabase.dbo.tableName)
You can't talk to two CF (JDBC) datasources in a single CFQUERY. What you can do:
Use two databases on the same datasource. For example, if you have a SQL Server instance with two database you can run a query through the JDBC connection that talks to both databases. This looks like what you're describing in your question. Here's a more thorough explanation.
Use Queries of Queries. Pull your data from the two database individually and join the results using a QoQ in your CFC or page.
ColdFusion can only talk to one data*source* at a time in a given query. However, if you need to talk to more than one data*base* on the same server, you can do that by explicitly giving the full paths to the databases, tables, and columns you need to access or join together. Also note that the user that the data*source* in ColdFusion is configured to use must have access to both databases in order for this to work.
Here's the situation: we have an Oracle database we need to connect to to pull some data. Since getting access to said Oracle database is a real pain (mainly a bureaucratic obstacle more than anything else), we're just planning on linking it to our SQL Server and using the link to access data as we need it.
For one of our applications, we're planning on making a view to get the data we need. Now the data we need is joined from two tables. If we do this, which would be preferable?
This (in pseudo-SQL if such a thing exists):
OPENQUERY(Oracle, "SELECT [cols] FROM table1 INNER JOIN table2")
or this:
SELECT [cols] FROM OPENQUERY(Oracle, "SELECT [cols1] FROM table1")
INNER JOIN OPENQUERY(Oracle, "SELECT [cols2] from table2")
Is there any reason to prefer one over the other? One thing to keep in mind: we are on a limitation on how long the query can run to access the Oracle server.
I'd go with your first option especially if your query contains a where clause to select a sub-set of the data in the tables.
It will require less work on both servers, assuming there are indices on the tables in the Oracle server that support the join operation.
If the inner join significantly reduces the total number of rows, then option 1 will result in much less network traffic (since you won't have all the rows from table1 having to go across the db link
What hamishmcn said applies.
Also, SQL Server doesn't really know anything about the indexes or statistics or cache kept by the oracle server. Therefore, the oracle server can probably do a much more efficient job with the join than the sql server can.