I am new to Postgresql and so far I have not found a way to drop a table from specific database. To give some context:
We are doing a synchronization from Oracle to PostgreSQL of 5 tables. In postgres I have a database SoloCopy and the schema is the default public. In the Postgresql instance we have also 2 more databases SoloSynch and postgres (the default one).
What I want to do is to select SoloCopy database and:
DROP TABLE public.table1;
When I do the above DROP statement table1 is deleted only from the database that was selected when opening SQL Query. But I want to specify the database before that and to be irrelevant from where the SQL Query was open. How can I do that?
I found an answer on my own. Setup can be found here:
Psql in Task Scheduler does not run a file script
Basically I needed to use PSQL and with the connection string there I connect to a specific DB, which I can drop the tables from. The details for PGPASSWORD and the .bat file I ended up creating are in the link above. Had to start everything from CMD and switch to psql from there.
Related
I have a funny question about PostgreSQL database: What happens if the postgres database is dropped?
dropdb postgres worked.
createdb postgres worked too.
psql worked.
But I thought the users would be lost. Yet the old users are still there.
So where are the users stored for the database and which implications does dropping the postgres database have?
PostgreSQL metadata are stored in catalog tables, which are in the pg_catalog schema. These are accessible like regular views and tables.
There are shared system catalog tables which are shared between all databases. These tables are not affected when databases are dropped.
pg_authid, the table where the users are stored, is one of those shared catalogs. This is because in PostgreSQL, users don't belong to a database, but to the whole database cluster.
You can list all shared catalog tables like this:
SELECT relname FROM pg_class
WHERE relisshared AND relkind = 'r';
In the documentation you can find more information about the system catalogs.
When connecting to a Postgres server, you always need to specify which database you want to connect to.
When you set up a new server, you need something to connect to before you can run your first CREATE DATABASE statement.
That's all the postgres database is: a dummy database to use as a connection target for admin commands. There's no data in there, and you're free to drop it and use a different one instead (though whoever inherits your system will probably not thank you for it...).
As gil.fernandes said in his answer, server-wide objects like users are accessible from every database, but aren't stored inside any database in particular.
I'm trying to rename a database in my Redshift cluster.
You cannot rename the database when you're connected to it so I've created a temporary database, reconnected with SQL Workbench to the temporary db and issued:
ALTER DATABASE olddb RENAME to newdb;
I get an error stating ERROR: database "olddb" is being accessed by other users [SQL State=55006]
I've checked who is connected and there appear to be some connections from user rdsdb to the database. I assume this is a service account that AWS Redshift use to perform maintenance tasks etc.
How can I rename the database when this superuser is connected?
Many thanks.
You cannot alter the name of (or delete!) the database that is created during the initial cluster creation. I don't believe this is mentioned in the docs but I've confirmed it with them.
We can change the database name which is already created.
Detailed steps on how to do
Connect to the old database and create a new database if you do not have another one already.
create database databasebasename
In this example, I will call the databasename as 'newdb'.
Connect to newdb using connecting string as, jdbc:redshift://.us-east-1.redshift.amazonaws.com:8192/newdb, with the same password and username of your superuser (or the other eligible users as mentioned above).
Now you can alter the database name. Substitute 'database_name_new' with the desired databasename.
alter database old-db-name rename to database_name_new;
If there are any active sessions, you'll have to kill them. To find the pid of active sessions:
select * from STV_SESSIONS where user_name='rdsdb';
Then to kill a session:
SELECT
pg_terminate_backend(<pid>)
FROM
pg_stat_activity
WHERE
-- don't kill my own connection!
procpid <> pg_backend_pid()
-- don't kill the connections to other databases
AND datname = '<old-db-name>';
Once complete, you can connect back to that new database using the new name in the connection string as
jdbc:redshift://<cluser-id>.us-east-1.redshift.amazonaws.com:8192/database_name_new
You can delete the temporary 'newdb'.
drop database databasebasename
That's possible now -- I just renamed the database that was created during the initial cluster creation.
We had a similar situation.
Step 1: Connect to the database which is not the one you are trying to rename. Check the same by executing SELECT CURRENT_DATABASE();.
Step 2: Execute the query below -
SELECT
ss.*, 'select pg_terminate_backend('||process||');'
FROM
stv_sessions ss
ORDER BY
db_name;
The output of the query will have a column at the end with the select statements. Execute those to kill the sessions.
Step 3(Optional): If you are not the owner of the database try to modify the ownership of the database -
ALTER DATABASE <database to be renamed>
OWNER TO <user which is going to do the rename>;
Step 4: Rename the database
I need to update a dababase from an other database... For this I need to search in existing database if the records exists, if not add... One of the database is locally stored in my computer, and the other one is on heroku... But I don't know how to access heroku database from my computer to create the inserts and to query if I have to insert or not...
Any idea how can I do something like this?
You can connect via any DB tool, e.g. Oracle SQL Developer with Postgres JDBC connector, to a Heroku Postgres DB. The parameters are listed in the GUI of postgres.heroku.com for your instance.
I have 2 dbs on two different servers.
How can I copy using psql all the missing rows from db1 table to db2 table ?
If this is not possible.. How can I copy the entire table ?
Can you use a contrib module? If so, how about trying dblink. More information here
This is not possible with psql directly using a single SQL statement because you cannot connect to two different servers at the same time.
The only way you can do it:
connect to db1
export the table contents using psql's \copy command (if you have access to the server, you can also use the SQL statement COPY
connect to db1
import the text file using \copy or COPY depending on where the input file is located
I am very new to Postgres and the main problem I have now is that I don't have an overview of my server. If you use something like pgadmin3 it's easy to browse and to get a general idea of the structure of the database.
So looking for some general commands that could help me discover my database server.
Very basic commands:
Connect to database with client console
psql dbname
Dump db tables
\d
Dump a table schema
\d table
List table content
select * from table
General help
\?
Source/Further info: https://www.postgresql.org/docs/current/static/app-psql.html