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Questions tagged [postgresql]

All versions of PostgreSQL. Add an additional version-specific tag like postgresql-11 if that context is important.

1105
votes
7answers
2.3m views

How do I list all databases and tables using psql?

I am trying to learn PostgreSQL administration and have started learning how to use the psql command line tool. When I log in with psql --username=postgres, how do I list all databases and tables? I ...
238
votes
4answers
435k views

How do I list all columns for a specified table

I'm looking for a precise piece of information in a database which I have no knowledge about. It's a 3rd party product, they are slow on answering some questions, and I know the data is lying inside ...
220
votes
3answers
117k views

How can I time SQL-queries using psql?

I would like to benchmark some SQL-queries agains my PostgreSQL database. Is there any way I can time SQL-queries using psql?
208
votes
4answers
400k views

How do I list all schemas in PostgreSQL?

When using PostgreSQL v9.1, how do I list all of the schemas using SQL? I was expecting something along the lines of: SELECT something FROM pg_blah;
160
votes
10answers
364k views

connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host

Hello I am trying to run a website sent to me but after doing so this error appeared connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host "4X.XXX.XX.XXX", user "userXXX", database "...
156
votes
2answers
348k views

How to insert values into a table from a select query in PostgreSQL?

I have a table items (item_id serial, name varchar(10), item_group int) and a table items_ver (id serial, item_id int, name varchar(10), item_group int). Now I want to insert a row into items_ver ...
140
votes
5answers
351k views

Granting access to all tables for a user

I'm new to Postgres and trying to migrate our MySQL databases over. In MySQL I can grant SELECT, UPDATE, INSERT, and DELETE privileges on a low privileged user and enable those grants to apply to all ...
116
votes
2answers
113k views

Granting a user account permission to create databases in PostgreSQL

How do I give a user account in PostgreSQL the ability to create and drop databases? Is there a way to do this with GRANT?
112
votes
6answers
287k views

List the database privileges using psql

I'm in the middle of a database server migration and I can't figure (after googling and searching here) how can I list the database privileges (or all the privileges across the server) on PostgreSQL ...
109
votes
11answers
131k views

How do I find PostgreSQL's data directory?

I forgot how I last time started postgres (it was months ago) and I don't remember where the data directory is located at. The postgres command seems to require to location. I'm on MacOsX if that ...
96
votes
11answers
79k views

SQL: SELECT All columns except some

Is there a way to SELECT all columns in a table, except specific ones? IT would be very convenient for selecting all the non-blob or non-geometric columns from a table. Something like: SELECT * -...
92
votes
4answers
119k views

Force drop db while others may be connected

I need to remove a database from a PostgreSQL DB cluster. How can I do it even if there are active connections? I need sort of a -force flag, that will drop all connections and then the DB. How can I ...
86
votes
4answers
79k views

Optimizing queries on a range of timestamps (two columns)

I use PostgreSQL 9.1 on Ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one integer property. There are additional columns in my ...
86
votes
3answers
83k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...
83
votes
6answers
10k views

Do stored procedures prevent SQL injection?

Is it true that stored procedures prevent SQL injection attacks against PostgreSQL databases? I did a little research and found out that SQL Server, Oracle and MySQL are not safe against SQL injection ...
82
votes
8answers
113k views

Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

I had to write a simple query where I go looking for people's name that start with a B or a D : SELECT s.name FROM spelers s WHERE s.name LIKE 'B%' OR s.name LIKE 'D%' ORDER BY 1 I was wondering ...
80
votes
3answers
27k views

Is a composite index also good for queries on the first field?

Let's say I have a table with fields A and B. I make regular queries on A+B, so I created a composite index on (A,B). Would queries on only A also be fully optimized by the composite index? ...
76
votes
2answers
134k views

How do I get the current unix timestamp from PostgreSQL?

Unix timestamp is the number of seconds since midnight UTC January 1, 1970. How do I get the correct unix timestamp from PostgreSQL? When comparing to currenttimestamp.com and timestamp.1e5b.de I ...
71
votes
4answers
52k views

Measure the size of a PostgreSQL table row

I have a PostgreSQL table. select * is very slow whereas select id is nice and quick. I think it may be that the size of the row is very large and it's taking a while to transport, or it may be some ...
66
votes
1answer
49k views

Postgres UPDATE … LIMIT 1

I have a Postgres database which contains details on clusters of servers, such as server status ('active', 'standby' etc). Active servers at any time may need to fail over to a standby, and I don't ...
65
votes
5answers
25k views

Working of indexes in PostgreSQL

I have a couple of questions regarding working of indexes in PostgreSQL. I have a Friends table with the following index: Friends ( user_id1 ,user_id2) user_id1 and user_id2 are foreign keys to ...
63
votes
4answers
89k views

How to get the name of the current database from within PostgreSQL?

Using \c <database_name> in PostgreSQL will connect to the named database. How can the name of the current database be determined? Entering: my_db> current_database(); produces: ERROR: ...
63
votes
3answers
64k views

How can I specify the position for a new column in PostgreSQL?

If I have a table with the columns: id | name | created_date and would like to add a column, I use: alter table my_table add column email varchar(255) Then the column is added after the ...
59
votes
5answers
128k views

How to turn json array into postgres array?

I have a column data that holds a json document roughly like this: { "name": "foo", "tags": ["foo", "bar"] } I would like to turn the nested tags array into a concatenated string (foo, bar). ...
58
votes
3answers
36k views

What are the drawbacks with using UUID or GUID as a primary key?

I would like to build a distributed system. I need to store data in databases and it would be helpful to use an UUID or a GUID as a primary key on some tables. I assume it's a drawbacks with this ...
57
votes
3answers
115k views

How to use psql with no password prompt?

I wrote a script to REINDEX indexes in a database. Here is one of them: echo -e "\nreindex for unq_vbvdata_vehicle started at: `date "+%F %T"`" >> ${LOG_FILE} psql -U ${USERNAME} -h ${HOSTNAME} ...
57
votes
2answers
56k views

Create index if it does not exist

I am working on a function that allows me to add an index if it does not exist. I am running into the problem that I cannot get a list of indexes to compare to. Any thoughts? This is a similar issue ...
57
votes
2answers
86k views

What is faster, one big query or many small queries?

I have been working for different companies, and I have noticed that some of them prefer to have views that will join a table with all its "relatives". But then on the application some times, we only ...
56
votes
3answers
62k views

Find highest level of a hierarchical field: with vs without CTEs

note: this question has been updated to reflect that we are currently using MySQL, having done so, I would like to see a how much easier it would be if we switched to a CTE-supporting database. I ...
53
votes
8answers
153k views

How do I use currval() in PostgreSQL to get the last inserted id?

I have a table: CREATE TABLE names (id serial, name varchar(20)) I want the "last inserted id" from that table, without using RETURNING id on insert. There seem to be a function CURRVAL(), but I don'...
52
votes
4answers
49k views

Can a single PostgreSQL query use multiple cores?

In recent versions of PostgreSQL (as of Dec 2013), can we share a query between two or more cores to get a performance boost? Or should we get faster cores?
48
votes
2answers
50k views

Default value for UUID column in Postgres

In Postgres 9.x, for a column of type UUID, how do I specify a UUID to be generated automatically as a default value for any row insert?
48
votes
4answers
149k views

How to run psql on Mac OS X?

I installed PostgreSQL on a computer with Mac OS X using the One click installer. Then I try to access PostgreSQL using the psql command, but it doesn't seem to be available. I get this message: ...
47
votes
6answers
108k views

How do I efficiently get “the most recent corresponding row”?

I have a query pattern that must be very common, but I don't know how to write an efficient query for it. I want to look up the rows of a table that correspond to "the most recent date not after" the ...
47
votes
6answers
16k views

Is it possible to quickly create/restore database snapshots with PostgreSQL?

First of all, I'm a developer, not a DBA or sysadmin; please be gentle :) I'm working on an application workflow where a single user action will trigger complex changes in the database - creating ...
46
votes
3answers
253k views

How do I insert a row which contains a foreign key?

Using PostgreSQL v9.1. I have the following tables: CREATE TABLE foo ( id BIGSERIAL NOT NULL UNIQUE PRIMARY KEY, type VARCHAR(60) NOT NULL UNIQUE ); CREATE TABLE bar ( id BIGSERIAL ...
42
votes
1answer
32k views

Scalability limitations of PostgreSQL and MySQL

I've heard that performance of non-sharded relational database such as MySQL or PostgreSQL "breaks" beyond 10 TB. I suspect that limits as such do exist as one would not come up with Netezza, ...
41
votes
3answers
43k views

How to run recurring tasks on Postgresql without an external cron-like tool?

I would like to call a stored procedure on a regular basis. On Oracle, I would create a job for this. I have found that Postgresql can mimic this well by using an external tool (cron etc) and PgAgent. ...
40
votes
4answers
28k views

Function Performance

Coming from a MySQL background, where stored procedure performance (older article) and usability are questionable, I am evaluating PostgreSQL for a new product for my company. One of the things I ...
40
votes
3answers
38k views

Created user can access all databases in PostgreSQL without any grants

I must be missing something with regards to setting up PostgreSQL. What I'd like to do is create multiple databases and users that are isolated from each other so that a specific user only has access ...
40
votes
1answer
58k views

How to get a working and complete PostgreSQL DB backup and test

I was hoping I could get a clear answer on how to ensure taking a full Postgres backup just like you would get with MS SQL Server, and then take care of orphaned users. From what I've read, and it ...
39
votes
1answer
19k views

Best practices for schema changes and data migrations to a live database without downtime?

How do you make schema changes to a live database without downtime? For instance, lets say I have a PostgreSQL database with a table including various user data like email addresses etc, all ...
38
votes
5answers
38k views

Aggressive Autovacuum on PostgreSQL

I'm trying to get PostgreSQL to aggressively auto vacuum my database. I've currently configured auto vacuum as follows: autovacuum_vacuum_cost_delay = 0 #Turn off cost based vacuum ...
37
votes
2answers
71k views

How to view data in pgAdmin III

I can't believe they make it this hard. I am at a loss about how to view the data in my database. Is there an easy way to see what data is in my tables with pgAdmin III? Alternatively, is there a ...
37
votes
2answers
34k views

Difference between now() and current_timestamp

In PostgreSQL, I use the now() and current_timestamp function and I see no difference: # SELECT now(), current_timestamp; now | now ------------...
37
votes
3answers
43k views

Idiomatic way to implement UPSERT in PostgreSQL

I've read about different UPSERT implementations in PostgreSQL, but all of these solutions are relatively old or relatively exotic (using writeable CTE, for example). And I'm just not a psql expert ...
37
votes
2answers
59k views

Increasing work_mem and shared_buffers on Postgres 9.2 significantly slows down queries

I have a PostgreSQL 9.2 instance running on RHEL 6.3, 8-core machine with 16GB of RAM. The server is dedicated to this database. Given that the default postgresql.conf is quite conservative regarding ...
36
votes
2answers
23k views

Can't rename columns in PostgreSQL views with CREATE OR REPLACE

In PostreSQL 8.3, I'm trying to create a view which will look just like an existing table but have different column names. This works CREATE OR REPLACE VIEW gfam.nice_builds AS SELECT (family_tree....
36
votes
4answers
18k views

Are views harmful for performance in PostgreSQL?

The following is an excerpt from a book about db design (Beginning Database Design ISBN: 0-7645-7490-6): The danger with using views is filtering a query against a view, expecting to read a very ...
35
votes
10answers
126k views

PostgreSQL not running on Mac

The error in its entirety reads: psql: could not connect to server: No such file or directory. Is the server running locally and accepting connections on Unix domain socket "/tmp/.s.PGSQL.5432"?...