Im trying to alter a table ALTER TABLE database.table...
What is the correct notation to access tables in a DB from the base postgres db without having to explicitly connect to that database?
There is no way. You have to connect to the right database.
A DATABASE within MySQL is comparable with a SCHEMA in PostgreSQL and many other brands.
MySQL: ALTER TABLE database.table...
Others: ALTER TABLE schema.table...
From the MySQL manual:
CREATE SCHEMA is a synonym for CREATE DATABASE.
This actually means that a single MySQL server has just a single database. This database can have many schema's and every schema can have many tables.
Within a single database you can jump from one schema to the other schema, no problem. This works for MySQL, PostgreSQL and many others. You can not jump from one database to another database without a new database connection because it's a different instance.
It is that MySQL uses a different name for a schema, it calls this a database. A little confusing.
If you want the same thing in other databases, like PostgreSQL, just use schema's within a single database.
Related
I have done some queries in a read-only (Oracle/SQL developer) dB where I have absolutely no privileges to create temporary tables or anything else. I want to export the tables resulting of my queries into another db (PostGre/pgAdmin) db in order to be able to do other queries on the result.
Is there an easy way to create the columns of my exported tables in the PostGre db using pgAdmin or do I have to create all the columns manually ?
You could install the Oracle Foreign Data Wrapper in your PostgreSQL database and use IMPORT FOREIGN SCHEMA to create foreign tables for your Oracle tables.
Then you can use
CREATE TABLE local_table AS SELECT * FROM foreign_table;
to copy the data.
Are we able to perform SQL operations like INSERT, UPDATE, DELETE to Database Catalog (It is more theory question than practice)
If a database supports INFORMATION_SCHEMA and provides instruments for altering the database catalog, then yes, you can use SQL operations normally.
For example, in PostgreSQL documentation you can read:
The system catalogs are the place where a relational database management system stores schema metadata, such as information about tables and columns, and internal bookkeeping information. PostgreSQL's system catalogs are regular tables. You can drop and recreate the tables, add columns, insert and update values, and severely mess up your system that way. Normally, one should not change the system catalogs by hand, there are always SQL commands to do that. (For example, CREATE DATABASE inserts a row into the pg_database catalog — and actually creates the database on disk.)
So, you change the catalog indirectly creating a new database. Nonetheless, with PostgreSQL you can directly change the catalog, using SQL commands like DROP, INSERT, UPDATE and so on.
Some RDBMS don't provide such a possibility, such as Oracle Database, IBM DB2, SQLite or Sybase ASE. Some RDBMS provide INFORMATION_SCHEMA, but it is read-only, so you can't do anything crazy, for example, MySQL. Its documentation reads:
Although you can select INFORMATION_SCHEMA as the default database with a USE statement, you can only read the contents of tables, not perform INSERT, UPDATE, or DELETE operations on them.
I've been told that RDBMS ( SQL Server in this case ) make use of the temporary database to perform its internal job, for instance when a SELECT count( column ) FROM foo query is performed.
What kind of queries / statements trigger the use of the temporary database?
background:
We are currently about to change the collation on our application database, but we have been told there might be problems if that database make use of the temporary database, because they will have different collation. The rationale is the temporary database is already being used by other applications.
So we want to identify what kind of queries may trigger temp db usage and see if they'll have any problem.
I've found this about when is the db used:
http://msdn.microsoft.com/en-us/library/ms190768.aspx
I did a succesful migration from MySql to Sql Server using the migration tool.
Unfortunately for some reason it labels the tables database.DBO.tablename instead of just database.tablename
I have never used Sql Server so perhaps this is just the way they name their tables.
When I do:
SELECT TOP 1000 [rid]
,[filename]
,[qcname]
,[compound]
,[response]
,[isid]
,[isidresp]
,[finalconc]
,[rowid]
FROM [test].[calibration]
it does not work
But, when I do:
SELECT TOP 1000 [rid]
,[filename]
,[qcname]
,[compound]
,[response]
,[isid]
,[isidresp]
,[finalconc]
,[rowid]
FROM [test].[dbo].[calibration]
it works.
Does anyone know why it prefixes with DBO?
dbo is the standard database owner for anything you create (tables, stored procedures, etc,..), hence the migration tool automatically prefixing everything with it.
When you access something in Sql Server, such as a table called calibration, the following are functionally equivalent:
calibration
dbo.calibration
database_name.dbo.calibration
server_name.database_name.dbo.calibration
MySql doesn't, as far as I remember (we migrated a solution from MySql to SqlServer about 12 months ago using custom scripts executed by nant) support database owner's when referencing objects, hence you're probably not familiar with four part (server_name.database_name.owner_name.object_name) references.
Basically, if you want to specify the database you're accessing, you also need to specify the "owner" of the object. i.e, the following are functionally identical:
USE [master]
GO
SELECT * FROM [mydatabase].[dbo].[calibration]
USE [mydatabase]
GO
SELECT * FROM [calibration]
SqlServer uses an owner name when it references tables. In this case, dbo is the owner.
MySQL doesn't use owner for table names, which is why you didn't see those names before.
SQL Server has something called schemas, in this case the default schema is dbo but it could be anything you wanted. Schemas are used to logically group objects. So you can create a Employee schema and have all the Employee tables, views, procs and functions in there, this then also enables you to give certain users only access to certain schemas
Tell me your migration tool you have used, and let me know the version of from and to databases.
Regards
Eugene
You do have an issue here with the default schema, if it's set to 'dbo' for the user you logged in as you don't need to specify it. See http://msdn.microsoft.com/en-us/library/ms176060.aspx
Is it possible to create more than one table at a time using single create table statement.
For MySQL, you can use multi-query to execute multiple SQL statements in a single call. You'd issue two CREATE TABLE statements separated by a semicolon.
But each CREATE TABLE statement individually can create only one table. The syntax supported by MySQL does not allow multiple tables to be created simultaneously.
#bsdfish suggests using transactions, but DDL statements like CREATE TABLE cause implicit transaction commits. There's no way to execute multiple CREATE TABLE statements in a single transaction in MySQL.
I'm also curious why you would need to create two tables simultaneously. The only idea I could come up with is if the two tables have cyclical dependencies, i.e. they reference each other with foreign keys. The solution to that is to create the first table without that foreign key, then create the second table, then add the foreign key to the first table with ALTER TABLE ADD CONSTRAINT. Dropping either table requires a similar process in reverse.
Not with MS SQL Server. Not sure about mysql.
Can you give more info on why you'd want to do this? Perhaps there's an alternative approach.
I don't know, but I don't think you can do that. Why you want to do this?
Not in standard SQL using just the 'CREATE TABLE' statement. However, you can write multiple statements inside a CREATE SCHEMA statement, and some of those statements can be CREATE TABLE statements. Next question - does your DBMS support CREATE SCHEMA? And does it have any untoward side-effects?
Judging from the MySQL manual pages, it does support CREATE SCHEMA as a synonym for CREATE DATABASE. That would be an example of one of the 'untoward side-effects' I was referring to.
(Did you know that standard SQL does not provide a 'CREATE DATABASE' statement?)
I don't think it's possible to create more than one table with a 'CREATE TABLE' command. Everything really depends on what you want to do. If you want the creation to be atomic, transactions are probably the way to go. If you create all your tables inside a transaction, it will act as a single create statement from the perspective of anything going on outside the transaction.