Questions tagged [postgresql]

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

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23
votes
1answer
2k views

Is the optimisation fence behaviour of a CTE (WITH query) specified in the SQL:2008 standard? If so, where?

I see frequent references to WITH queries (common table expressions, or CTEs) acting as an optimisation fence, where the server isn't permitted to push filters down into the CTE queries, pull common ...
22
votes
3answers
8k views

How is LIKE implemented?

Can anyone explain how the LIKE operator is implemented in current database systems (e.g. MySQL or Postgres)? or point me to some references that explain it? The naive approach would be to inspect ...
22
votes
3answers
21k views

How to choose a collation for international database?

I'm designing a database which will store data in different languages (using UTF-8), so I think the best way to display the query's results is ordering it according to the user's language during the ...
22
votes
2answers
40k views

How to set Postgresql database to see date as “MDY” permanently

How can I set my database to see the 'date' as "MDY" without running: SET datestyle = "ISO, MDY"; every-time I'm trying to access it? I'm using Postgresql version 9.1, Ubuntu 12.04. My system locale,...
22
votes
2answers
15k views

What happens in PostgreSQL checkpoint?

Here's part of my checkpoint log: 2014-03-26 11:51:29.341 CDT,,,18682,,532854fc.48fa,4985,,2014-03-18 09:15:24 CDT,,0,LOG,00000,"checkpoint complete: wrote 15047 buffers (1.4%); 0 transaction log ...
22
votes
2answers
11k views

How to store time series data

I have what I believe is a time series data set (please correct me if I'm wrong) that has a bunch of associated values. An example would be modeling a car and tracking its various attributes during a ...
22
votes
1answer
53k views

How to connect to an remote PostgreSQL database on Ubuntu using pgAdmin3?

I'm trying to setup a PostgreSQL database on an Ubuntu machine. I would like to be able to access it using pgAdmin3 from a remote machine. How do I setup this? I have installed the PostgreSQL ...
22
votes
5answers
51k views

PostgreSQL: How to backup only One Schema from a database and restore it on another server

I have a database named "A" which has two schemas "B" and "C". I want to backup and restore Schema "B" on a different server? not sure how to do this as I am new to Postgres. Do I have to create a new ...
22
votes
1answer
6k views

Is there a good way to run a trigger for each record in a postgres table?

I have a system where I can't control the design of some tables (replicated via Slony-I), and so I have a series of what we refer to as 'shadow tables', where I extract some information out of the ...
22
votes
2answers
5k views

What is the modern way to partition PostgreSQL across machines, when the data is “naturally partitionable”

After several years of dwelling into the "NoSQL" space, now I have a problem that is quite "relational" in its nature. Today I see data stores with quite different eyes than before. Things like Riak ...
21
votes
2answers
57k views

PgAdmin III - How to connect to database when password is empty?

I have installed PostgreSQL 9.1 on my PC (Win 7). I have a small Java application connecting successfully to it with login=sa and password="". The connection works. However, it is refused from ...
21
votes
2answers
311k views

Using SELECT in the WHERE clause of another SELECT

I have made a draft remote application on top of libpq for PostrgreSQL. It behaves well, but I have profiled the general functioning of the application. For each final business result that I produce, ...
21
votes
1answer
38k views

Number of active connections and remaining connections

I would like to get statistics about the peak number of connections over a period of time. I know the pg_stat_activity view, like select count(*) from pg_stat_activity, but I think this method is not ...
21
votes
3answers
12k views

Running pg_dump on a hot standby server?

Disclaimer: I admittedly haven't tried this yet, but I'm not sure I would know if it wasn't working correctly, so I wanted to ask. I would like to run a nightly backup job (via pg_dumpall) from a hot ...
21
votes
1answer
25k views

VACUUM returning disk space to operating system

VACUUM usually does not return disk space to operating system, except in some special cases. From the docs: The standard form of VACUUM removes dead row versions in tables and indexes and marks the ...
21
votes
1answer
13k views

Why does NOT IN with a set containing NULL always return FALSE/NULL?

I had a query (for Postgres and Informix) with a NOT IN clause containing a subquery that in some cases returned NULL values, causing that clause (and the entire query) to fail to return anything. ...
21
votes
5answers
124k views

Query to return output column names and data types of a query, table or view

Is there a PostgreSQL query or command that returns the field names and field types of a query, table or view? E.g., a solution if applied to simple SELECT query like SELECT * from person should ...
21
votes
3answers
20k views

In PostgreSQL, is there a type-safe first() aggregate function?

Full question re-write I'm looking for a First() aggregate function. Here I found something that almost works: CREATE OR REPLACE FUNCTION public.first_agg ( anyelement, anyelement ) RETURNS ...
21
votes
2answers
9k views

“Recheck Cond:” line in query plans with a bitmap index scan

This is a spin-off from comments to the previous question: Postgres 9.4.4 query takes forever Using PostgreSQL 9.4, there always seems to be a Recheck Cond: line after bitmap index scans in query ...
21
votes
3answers
40k views

Can I provide a default for a left outer join?

Suppose I have tables a (with column a1) and b (with columns b1 and b2) and I perform a left outer join SELECT * FROM a LEFT OUTER JOIN b ON a.a1 = b.b1 Then b1 and b2 will be NULL where a value of ...
21
votes
2answers
20k views

Can I select data inserted in the same uncommited transaction?

Maybe this is a dumb beginner question, but I cannot find an answer anywhere. Everywhere I read about the Transaction Isolation which solves the visibility of data within the concurrent transactions. ...
20
votes
6answers
55k views

Select columns inside json_agg

I have a query like: SELECT a.id, a.name, json_agg(b.*) as "item" FROM a JOIN b ON b.item_id = a.id GROUP BY a.id, a.name; How can I select the columns in b so I don't have b.item_id in the ...
20
votes
6answers
19k views

Are there any good and free tools for managing a PostgreSQL database? [closed]

Before, I have used phpmyadmin to manage an MySQL database, but now I would like to manage a PostgreSQL database. The PostgreSQL database is on a server, but not a webserver, so I don't use PHP. Are ...
20
votes
1answer
43k views

Performance difference between MySQL and PostgreSQL for the same schema/queries [closed]

I'm a newbie DBA, and I have experience in Microsoft SQL Server but I want to jump to FLOSS. I'm starting a company, and we develop an app (PHP) with a Postgres backend, and we did some tests ...
20
votes
2answers
20k views

Query the definition of a materialized view in Postgres

I'm wondering how to query the definition of a materialized view in Postgres. For reference, what I hoped to do is very similar to what you can do for a regular view: SELECT * FROM information_schema....
20
votes
2answers
8k views

PostgreSQL procedural languages - differences between PL/pgSQL and SQL

Can anybody please summarize the differences between: http://www.postgresql.org/docs/9.1/static/xfunc-sql.html and http://www.postgresql.org/docs/9.1/static/plpgsql.html ? Main points: ...
20
votes
6answers
4k views

Count where two or more columns in a row are over a certain value [basketball, double double, triple double]

I play a basketball game which allows to output its statistics as a database file, so one can calculate statistics from it that are not implemented in the game. So far I've had no problem caluclating ...
20
votes
4answers
7k views

Combining separate ranges into largest possible contiguous ranges

I'm trying to combine multiple date ranges (my load is about max 500, most cases 10) that may or may not overlap into the largest possible contiguous date ranges. For example: Data: CREATE TABLE ...
20
votes
7answers
32k views

How to convert a MySQL database to PostgreSQL?

Is there any command line tool for converting the MySQL database to PostgreSQL? I'd also like to know if there is a way to convert the database using the normal mysqldump command.
20
votes
2answers
12k views

How to create an index to speed up an aggregate LIKE query on an expression?

I may be asking the wrong question in the title. Here are the facts: My customer service folk have been complaining about slow response times when doing customer lookups on the administration ...
20
votes
1answer
26k views

What is the meaning of n_live_tup and n_dead_tup in pg_stat_user_tables

What is the meaning of n_live_tup and n_dead_tup in pg_stat_user_tables or pgstattuple?
20
votes
1answer
69k views

Rolling sum / count / average over date interval

In a database of transactions spanning 1,000s of entities over 18 months, I would like to run a query to group every possible 30-day period by entity_id with a SUM of their transaction amounts and ...
20
votes
3answers
18k views

Moving postgresql data to different drive

I am using AWS as my cloud environment. I installed PostgreSQL on the same drive as my root instance volume. I have attached and mounted the second drive to my instance. Now I want to move all my ...
20
votes
5answers
15k views

Best cloud platform for PostgreSQL [closed]

Currently, in our project, we use dedicated servers for our PostgreSQL database. In theory, we can run anything on some cloud platforms. However, PostgreSQL configuration is strictly related to ...
20
votes
3answers
28k views

How to optimization database for heavy I/O from updates (software and hardware)

The situation I have a postgresql 9.2 database which is quite heavily updated all the time. The system is hence I/O bound, and I'm currently considering making another upgrade, I just need some ...
20
votes
3answers
23k views

How to get notices to the output stream?

I have debugging messages in functions. Those message are raised like RAISE NOTICE 'Value of id : %', id; I set my log file with \o messages.txt Then I do what I need to do with \i process.sql And ...
19
votes
1answer
106k views

How can I convert a string to a double precision in PostgreSQL? [closed]

How can I convert a string to a double precision in PostgreSQL ? I tried something like : update points set latitude2 = cast(latitude as double) ; where latitude is a string and latitude2 is a ...
19
votes
4answers
25k views

Find IDs from a list that don't exist in a table

Say I have the following schema and data: create table images( id int not null ); insert into images values(1), (2), (3), (4), (6), (8); I want to perform a query like: select id from images ...
19
votes
2answers
20k views

PostgreSQL maximize performance SSD

I will have a huge PostgreSQL 9.3 database with many tables with more than 100M entries per table. This database will be basically be read-only (once I fill all the necessary tables and build the ...
19
votes
2answers
11k views

Is a Postgres long-running query aborted if the connection is lost/broken?

If I open a connection to Postgres and issue a long-running query, and then break the connection (e.g., kill the client process that opened the connection), will the long-running query continue to run,...
19
votes
2answers
6k views

Postgres query plan of a function invocation written in plpgsql

It's possible when using the pgadmin or plsql to get a hold of a query plan for a sql statement executed inside a user defined function (UDF) using EXPLAIN. So how do I get hold of the query plan for ...
19
votes
2answers
33k views

How to best store a timestamp in PostgreSQL?

I'm working on a PostgreSQL DB design and I am wondering how best to store timestamps. Assumptions Users in different timezones will use the database for all CRUD functions. I have looked at 2 ...
19
votes
3answers
30k views

Postgresql doesn't accept replication connection

Plain old streaming replication. PostgreSQL: 9.2.7 Windows 8.1 64 bit My primary and secondary clusters are on same windows machine. I have already done pg_start_backup() and everything, so both ...
19
votes
3answers
30k views

PostgreSQL using count() to determine percentages (cast issues)

I'm trying to run the following query to provide the % of rows in my patients table that have a value the refinst column. I keep getting a result of 0. select (count (refinst) / (select count(*) from ...
19
votes
6answers
42k views

PostgreSQL Change owner of all tables under a specific schema

I am trying to change the owner of all tables under the same schema in one command line. i.e: alter table schema_name.* owner to newowner. Is there a way to accomplish that?
19
votes
1answer
25k views

ERROR: database “dbname” does not exist

According to the documentation, so long as I'm not connected to a database, I can either delete a database in the console using: DROP DATABASE dbname; Or I can drop it using the wrapper tool dropdb. ...
19
votes
2answers
31k views

How to partition existing table in postgres?

I would like to partition a table with 1M+ rows by date range. How is this commonly done without requiring much downtime or risking losing data? Here are the strategies I am considering, but open to ...
19
votes
7answers
8k views

Efficiently select beginning and end of multiple contiguous ranges in Postgresql query

I've got about a billion rows of data in a table with a name and an integer in the range 1-288. For a given name, every int is unique, and not every possible integer in the range is present--so there ...
19
votes
3answers
9k views

PostgreSQL: Can I do pg_start_backup() on a live, running db under load?

Our established replication has broken ("requested WAL segment has already been removed" during downtime) We cannot easily stop the master again. Can we do pg_start_backup(), rsync ${PGDATA}/ ...
19
votes
2answers
2k views

Why are the plans different if the queries are logically alike?

I wrote two functions to answer Day 3's first homework question from Seven Databases in Seven Weeks. Create a stored procedure where you can input a movie title or actor's name you like, and it ...