Is there a SQL command that will list all the tables in a database and which is provider independent (works on MSSQLServer, Oracle, MySQL)?
The closest option is to query the INFORMATION_SCHEMA for tables.
SELECT *
FROM INFORMATION_SCHEMA.Tables
WHERE table_schema = 'mydatabase';
The INFORMATION_SCHEMA is part of standard SQL, but not all vendors support it. As far as I know, the only RDBMS vendors that support it are:
MySQL
PostgreSQL
Microsoft SQL Server 2000/2005/2008
Some brands of database, e.g. Oracle, IBM DB2, Firebird, Derby, etc. have similar "catalog" views that give you an interface where you can query metadata on the system. But the names of the views, the columns they contain, and their relationships don't match the ANSI SQL standard for INFORMATION_SCHEMA. In other words, similar information is available, but the query you would use to get that information is different.
(footnote: the catalog views in IBM DB2 UDB for System i are different from the catalog views in IBM DB2 UDB for Windows/*NIX -- so much for the Universal in UDB!)
Some other brands (e.g. SQLite) don't offer any queriable interface for metadata at all.
No. They all love doing it their own little way.
No, the SQL standard does not constrain where the table names are listed (if at all), so you'll have to perform different statements (typically SELECT statements on specially named tables) depending on the SQL engine you're dealing with.
If you are OK with using a non-SQL approach and you have an ODBC driver for the database and it implements the SQLTables entry-point, you possibly might get the information you want!
pjjH
details on the API at:
http://msdn.microsoft.com/en-us/library/ms711831.aspx
Related
I'm very excited by several of the more recently-added Postgres features, such as foreign data wrappers. I'm not aware of any other RDBMS having this feature, but before I try to make the case to my main client that they should begin preferring Postgres over their current cocktail of RDBMSs, and include in my case that no other database can do this, I'd like to verify that.
I've been unable to find evidence of any other database supporting SQL/MED, and things like this short note stating that Oracle does not support SQL/MED.
The main thing that gives me doubt is a statement on http://wiki.postgresql.org/wiki/SQL/MED:
SQL/MED is Management of External Data, a part of the SQL standard that deals with how a database management system can integrate data stored outside the database.
If FDWs are based on SQL/MED, and SQL/MED is an open standard, then it seems likely that other RDBMSs have implemented it too.
TL;DR:
Does any database besides Postgres support SQL/MED?
IBM DB2 claims compliance with SQL/MED (including full FDW API);
MySQL's FEDERATED storage engine can connect to another MySQL database, but NOT to other RDBMSs;
MariaDB's CONNECT engine allows access to various file formats (CSV, XML, Excel, etc), gives access to "any" ODBC data sources (Oracle, DB2, SQLServer, etc) and can access data on the storage engines MyIsam and InnoDB.
Farrago has some of it too;
PostgreSQL implements parts of it (notably it does not implement routine mappings, and has a simplified FDW API). It is usable as readeable since PG 9.1 and writeable since 9.3, and prior to that there was the DBI-Link.
PostgreSQL communities have a plenty of nice FDW like noSQL FDW (couchdb_fdw, mongo_fdw, redis_fdw), Multicorn (for using Python output instead of C for the wrapper per se), or the nuts PGStrom (which uses GPU for some operations!)
SQL Server has the concept of Linked Servers (http://technet.microsoft.com/en-us/library/ms188279.aspx), which allows you to connect to external data sources (Oracle, other SQL instances, Active Directory, File system data via the Indexing Service provider, etc.) and, if you really needed to, you can create your own Providers that can be used by a SQL Server Linked Server.
Another option within SQL Server is the CLR, in which you can write code to retrieve data from web services or other data sources as needed.
While this may not technically be "SQL/MED", it seems to accomplish the same thing.
Distributed query using local table joined to 4-part linked server query. I think case the remotetable filter might not be applied until after the entire table is pulled local (documentation is fuzzy on this and I've found article with conflicting opinions):
SELECT *
FROM LocalDB.dbo.table t
INNER JOIN LinkedServer1.RemoteDB.dbo.remotetable r on t.val = r.val
WHERE r.val < 1000
;
Using OpenQuery, remotetable filter is applied on the remote server, as long as the filter is passed into the OpenQuery 2nd parameter:
SELECT *
FROM LocalDB.dbo.table t
INNER JOIN OPENQUERY(LinkedServer1, 'SELECT * FROM RemoteDB.dbo.remotetable r WHERE r.val < 1000') r on t.val = r.val
I have two different databases (on same server) and i want to join tables across databases. I am using Hibernate, is it possible to create a query in hibernate which can join two tables in those databases?
Hibernate will create an SQL query for your HQL or Criteria query and this SQL will be sent through jdbc to the database. This means that hibernate does not support for what you are trying to do.
However, you can achieve the same result in some cases. Some databases give you the option to create an alias for a table that resides in a different database. So you will be able to write an SQL query that joins the two tables and execute it on the database.
We are doing that with DB2.
If you can do that, it depends on your database.
I guess, that it would impossible if you have two different databases (example DB2 and MySQL) but if both databases are of the same vendor, then maybe it's achievable.
You should try to find more info in you database server's documentation.
I have a local (read and write) sqlite database and a remote (read-only) oracle database. I use ODBC to access both DBs (I use an application to access the DBs by ODBC and query as such: EXECUTE-QUERY SQLITE "SELECT ..." or EXECUTE-QUERY ORACLE "SELECT ...") . I tried searching the net for a way to be able to perform one query joining tables from the 2 databases, but all I find is how to create a database link from oracle to other DBs but that doesn't help me because I have no write priviledges for the Orcale DB so creations of database links, databases, tables, views are not allowed in ORACLE, all I can do is query there. Is there an efficient way to do this with the restraints that I have?
How big are the tables in oracle? Given the limits of the access you have and the technology you are working with ( sqlite and oracle are worlds apart ), your best bet would probably be to export the tables from oracle into sqlite, then do your queries all within that.
Finally I installed Oracle express edition and created a database link to the other (read-only) oracle database. That worked great.
This is a question about Sql generation, not sql creating sql nor ORM.
Is their any cross database tools that will enable the creation of insert statements, e.g. for all the tables in particular schema or namespace. Say the namespace/schema is Aqua in Sql Server 2008, and your utility comes along and generates all possible insert statements for that namespace/schema. And it works on Oracle/MySql/Postgres/db2 etc.
Thanks.
Bob
ANSI SQL provides for a standard set of views under the schema INFORMATION_SCHEMA to provide metadata for just this purpose.
For generating simple table insert statement templates, all the information you really need to generate an insert statement for a given table is to execute this query:
select *
from INFORMATION_SCHEMA.COLUMNS
where TABLE_CATALOG = <my-db-name>
and TABLE_SCHEMA = <table-owner-schema>
and TABLE_NAME = <table-name>
order by ORDINAL_POSITION
in any database that supports the ANSI information schema views. That will give you one row for every column in the specified table, in the expected sequence.
Outside of the above, since no two vendors support the set of system tables with metadata, your pretty much SOL for a cross-database solution. And sadly, I don't believe the Oracle supports the ANSI information schema views.
Though you might look at Red Gate's product family: http://www.red-gate.com/
is there a way to create a select statement that would retrieve data from multiple database in postgre?
i was thinking it would be something like this:
select * from dbname1.table1, dbname2.table2 where dbname1.table1.column1 = dbname2.table2.column1
Have a look at the "dblink" contrib module.
OTOH it's possible that you treat the databases in a PostgreSQL cluster as equivalent to the databases in... let's say MySQL. Which is incorrect - the PostgreSQL databases contain schemas and those are the equivalent of the databases in MySQL.
From here:
It is not possible to access more than
one database per connection.
Update: but see Milen's answer.