I installed an application that uses a postgreSQL server but I don't know the name of the database and the tables it uses. Is there any command in order to see the name of the database and the tables of this application?
If you are able to view the database using the psql terminal command:
> psql -h hostname -U username dbname
...then, in the psql shell, \d ("describe") will show you a list of all the relations in the database. You can use \d on specific relations as well, e.g.
db_name=# \d table_name
Table "public.table_name"
Column | Type | Modifiers
---------------+---------+-----------
id | integer | not null
... etc ...
Using the psql on Linux you can use the \l command to list databases, \c dbname to connect to that db and the \d command to list tables in the db.
Short answer: connect to the default database with psql, and list all databases with '\l'
Then, connect to you database of interest, and list tables with '\dt'
Slightly larger answer: A Postgresql server installation usually has a "data directory" (can have more than one, if there are two server instances running, but that's quite unusual), which defines what postgresl calls "a cluster". Inside it, you can have several databases ; you usually have at least the defaults 'template0' and 'template1', plus your own database(s).
Related
And I want to know the details about template0 and template1 database
\l
Lists the databases. You can also run \list with similar results. See the documentation.
\d
stands for describe and shows the list of tables and other relations in the database.
Basically you need to switch to the database of your interest first, via running
\c template0
or
\c template1
depending where you want to connect and then run
\d
to list the tables in the current database. Since you do not specify a pattern in the above, it will display everything.
Now, if you are interested to see table structures, run \d tablename
Running
\dt+ *.*
will display all tables.
I need to play around with a data syncing program I wrote, but I want to copy the structure of the production database into a new table on my localhost Postgres database, without copying the data to my localhost db.
I was thinking along the lines of
CREATE TABLE new_table AS
TABLE existing_table
WITH NO DATA;
But I am unsure how to modify it to work with 2 different databases.
Any help would be appreciated
This boils down to the question "how to create the DDL script for a table" which can easily be done using pg_dump on the command line.
pg_dump -d some_db -h production_server -t existing_table --schema-only -f create.sql
The file create.sql then contains the CREATE TABLE script that you can run on your local Postgres installation.
I have tables from different databases , and i want to create a data warehouse database that contains table replicas from different tables from different databases. I want the data in the warehouse to be synced with the data from the other tables everyday.I am using postgresql
I tried to do this using psql :
pg_dump -t table_to_copy source_db | psql target_db
However it didnt work as it keeps stating errors like table does no exist.
It all worked when i dumped the whole dabatase not only a single table, but however i want the data to be synced and i want to copy tables from different databases not the whole database.
How can i do this?
Thanks!
Probably you need FDW - Foreign Data Wrapper. You can create foreign tables for different external db in different schemas on local db. All tables accessible by local queries. For storing snap you can use local tables with just INSERT INTO local_table_YYYY_MM SELECT * FROM remote_table; .
1
pg_dump -t <table name> <source DB> | psql -d <target DB>
(Check the table name correctly and it says for you , table doesn't exist)
2
pg_dump allows the dumping of only select tables:
pg_dump -Fc -f output.dump -t tablename databasename
(dump 'tablename' from database 'databasename' into file 'output.dump' in pg_dumps binary custom format)
You can restore that pg_restore:
pg_restore -d databasename output.dump
If the table itself already exists in your target database, you can import only the rows by adding the --data-only flag.
Dblink
You can not perform cross database query like SQL Server, PostgreSQL does not support this. DbLink extension of PostgreSQL which is used to connect one database to another database. You have to install and configure DbLink to execute cross database query.
Here is the step by step script and example for executing cross database query in PostgreSQL. Please visit this post:
I have around 150 MySQL databases, I need to export 1 table from each of the databases.
Is this possible, username and password are identical for each DB.
I'm sure there's a more compact way to do it but this should work.
#!/bin/bash
mysql -B -e "show databases" | egrep -v "Database|information_schema" | while read db;
do
echo "$db";
mysqldump $db TableName > $db.sql
done
You may need to tweak the mysql and mysqldump calls depending on your connection information.
I think in this case, iteration would be more appropriate (rather than recursion).
If you are on Linux, I'd suggest writing a simple bash script that cycles the 150 DB URLs and calls mysqldump on each one.
See link text, it generates meta data for all databases and all tables, you may be able to adapt it to export data for you. However this is in PHP and I am not certain of the language you wish to use..
Is there a simple way to create a copy of a database or schema in PostgreSQL 8.1?
I'm testing some software which does a lot of updates to a particular schema within a database, and I'd like to make a copy of it so I can run some comparisons against the original.
If it's on the same server, you just use the CREATE DATABASE command with the TEMPLATE parameter. For example:
CREATE DATABASE newdb WITH TEMPLATE olddb;
pg_dump with the --schema-only option.
If you have to copy the schema from the local database to a remote database, you may use one of the following two options.
Option A
Copy the schema from the local database to a dump file.
pg_dump -U postgres -Cs database > dump_file
Copy the dump file from the local server to the remote server.
scp localuser#localhost:dump_file remoteuser#remotehost:dump_file
Connect to the remote server.
ssh remoteuser#remotehost
Copy the schema from the dump file to the remote database.
psql -U postgres database < dump_file
Option B
Copy the schema directly from the local database to the remote database without using an intermediate file.
pg_dump -h localhost -U postgres -Cs database | psql -h remotehost -U postgres database
This blog post might prove helpful for you if you want to learn more about options for copying the database using pg_dump.
This can be done by running the following command:
CREATE DATABASE [Database to create] WITH TEMPLATE [Database to copy] OWNER [Your username];
Once filled in with your database names and your username, this will create a copy of the specified database. This will work as long as there are no other active connections to the database you wish to copy. If there are other active connections you can temporarily terminate the connections by using this command first:
SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = '[Database to copy]'
AND pid <> pg_backend_pid();
A good article that I wrote for Chartio's Data School which goes a bit more in depth on how to do this can be found here:
https://dataschool.com/learn/how-to-create-a-copy-of-a-database-in-postgresql-using-psql