In postgres, you specifiy a search path for the user you connect as and make sure that have the appropriate access rights to objects in other schemas, and that the other schemas exist in your search path so that the objects can be located.
In Oracle the same effect is achieved using synonyms. If a (public) synonym exists in your schema for an object in another schema then you can reference the object by the synonym name - especially if you make the synonym name the same as the destination object that it refers to. (A synonym can be considered to be like a symbolic link in unix).
The upshot is that you can write your SQL to reference objects without the schema prefix if you wish.
John Sidney-Woollett
Andrew Rawnsley wrote:
On Jun 9, 2004, at 5:15 PM, Dennis Gearon wrote:
This post is as much about getting some questions answered as leaving the following definitions in the archives for the next person.
After a quick perview of the web, I came up with the following:
tablespaces are a hardware issue, and totally transparent to SQL execution. It is for optimization for IO, recovery, and separating user and application usage amongst disks even in the same databases.
A bit more like database configuration based upon your hardware/design requirements and availability, but yes, its transparent to the guy writing the SQL. In Oracle (Sorry to use the 'O' word on the list...), you specify a tablespace when you create a table (or it uses a default one), but after that it only matters to the DBA actually running the installation.
schemas are a logical issue, and NOT transparent to the SQL. If schemas are involved, the SQL needs to know which schema tables are in to access them.
Yep.
My questions are: 1/ Am I right/
As much as makes no odds, yes.
2/ is the use of the '.' character standard across all databases as a schema delimiter, i.e. SELECT * FROM {schemaname.tablename.columnname;} ?
Yep.
3/ Once a user/dba gets down to the actual SQL, and past all the bl***ng Oracle Obfuscation(TM), does Oracle do the same thing with schemas that Postgres does, i.e. the aforementioned '.' separator?
Schemas are users in Oracle, but the net effect to the SQL author is the same. 'SELECT * FROM SERVICES.USERS' is the same, just that 'SERVICES' is a user in oracle (although referred to as a schema, and you have to do a 'CREATE SCHEMA AUTHORIZATION blablabla' to get anything to work. See your Oracle Obfuscation(TM) documentation, which of course will tell you nothing without the decoder ring that comes with a $10,000 service contract), and a schema in Postgres. Sybase and DB2 IIRC float in the middle with the terminology, but again, same effect to the author (the poor sod actually implementing the thing has to pay attention to all the differences, of course).
I am building an application that I want to work on Postgres, IBM DB2, Oracle, MSSQL, et.al.
If you keep your SQL generic, its not really that hard to do if you have/write decent middleware. The temptation is always to cheat and take advantage of native doodads to help things along.
TIA, y'all.
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Andrew Rawnsley President The Ravensfield Digital Resource Group, Ltd. (740) 587-0114 www.ravensfield.com
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