I need to migrate a mysql table to postgresql.
I need an accent and case insensitive database.
In mysql, my database has the next definition:
CREATE DATABASE gestan
DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
How do I create an equivalent definition to postgresql?
I have read some posts, but it seems outdated.
create database getan
encoding = 'UTF-8';
There is no direct equivalent for the case insensitive collation _ci in Postgres.
You can define a new ICU collation that uses case insensitive comparison, but it can't be used as a default collation for a database, only for the collation on column level.
Related questions:
Install utf8 collation in PostgreSQL
https://dba.stackexchange.com/questions/183355
https://dba.stackexchange.com/a/256979
I have a Postgres 9.3 database which, by mistake, has been set to:
but I need it to be:
Since the Encoding doesn't change, it is safe to dump the DB and restore it later (see here) to a database with the new Collation / Character type?
Perfectly safe -- the collation is just telling Postgres which set of rules to apply when sorting text.
You can even set it dynamically on a query basis in the order by clause, and should be able to alter it without needing to dump the database.
I'm using postgreSQL 9.1
I've set the Collation and the Character Type of the database to Greek_Greece.1253 and I want to change it to utf8
To change the collation I should use this, right?
But how can I change the character type?
Thanks
EDIT
I ment to wright C instead of utf8. I would like to change the Collation and the Character Type to C
You cannot change default collation of an existing database. You need to CREATE DATABASE with the collation you need and then dump/restore your schema and data into it.
If you do not want to recreate the database - you can specify collation for every text collumn in your db.
Here is detailed postgres manual on collations: Collation Support.
First line of this manual page states:
LC_COLLATE and LC_CTYPE settings of a database cannot be changed after
its creation.
CREATE DATABASE, pg_dump, pg_restore
In several SO posts OP asked for an efficient way to search text columns in a case insensitive manner.
As much as I could understand the most efficient way is to have a database with a case insensitive collation. In my case I am creating the database from scratch, so I have the perfect control on the DB collation. The only problem is that I have no idea how to define it and could not find any example of it.
Please, show me how to create a database with case insensitive collation.
I am using postgresql 9.2.4.
EDIT 1
The CITEXT extension is a good solution. However, it has some limitations, as explained in the documentation. I will certainly use it, if no better way exists.
I would like to emphasize, that I wish ALL the string operations to be case insensitive. Using CITEXT for every TEXT field is one way. However, using a case insensitive collation would be the best, if at all possible.
Now https://stackoverflow.com/users/562459/mike-sherrill-catcall says that PostgreSQL uses whatever collations the underlying system exposes. I do not mind making the OS expose a case insensitive collation. The only problem I have no idea how to do it.
A lot has changed since this question. Native support for case-insensitive collation has been added in PostgreSQL v12. This basically deprecates the citext extension, as mentioned in the other answers.
In PostgreSQL v12, one can do:
CREATE COLLATION case_insensitive (
provider = icu,
locale = 'und-u-ks-level2',
deterministic = false
);
CREATE TABLE names(
first_name text,
last_name text
);
insert into names values
('Anton','Egger'),
('Berta','egger'),
('Conrad','Egger');
select * from names
order by
last_name collate case_insensitive,
first_name collate case_insensitive;
See https://www.postgresql.org/docs/current/collation.html for more information.
There are no case insensitive collations, but there is the citext extension:
http://www.postgresql.org/docs/current/static/citext.html
For my purpose the ILIKE keyword did the job.
From the postgres docs:
The key word ILIKE can be used instead of LIKE to make the match
case-insensitive according to the active locale. This is not in the
SQL standard but is a PostgreSQL extension.
This is not changing collation, but maybe somebody help this type of query, where I was use function lower:
SELECT id, full_name, email FROM nurses WHERE(lower(full_name) LIKE '%bar%' OR lower(email) LIKE '%bar%')
I believe you need to specify your collation as a command line option to initdb when you create the database cluster. Something like
initdb --lc-collate=en_US.UTF-8
It also seems that using PostgreSQL 9.3 on Ubuntu and Mac OS X, initdb automatically creates the database cluster using a case-insensitive collation that is default in the current OS locale, in my case, en_US.UTF-8.
Could you be using an older version of PostgreSQL that does not default to the host locale? Or could it be that you are on an operating system that does not provide any case-insensitive collations for PostgreSQL to choose from?
I try to migrate to postgres from pervasive. In pervasive there was something like 'upper.alt' - alternative collation. I don't really know how it works, but I have to make my new postgres database to behave like pervasive with this collation.
I use Postgres 9.2.4 and utf-8 encoding and LC_COLLATE='Polish_Poland.1250' .
You can try and order with COLLATE "C". That would get what you want in your example. It has side effects though! Effectively everything is ordered according to the byte values of the encoded character.
WITH x(col) AS (
VALUES
('ABC_AAAAA')
,('ABC_BBBBB')
,('ABC_ZZZZZ')
,('ABCAAAAA')
,('ABCBBBBB')
,('ABCZZZZZ')
)
SELECT *
FROM x
ORDER BY col COLLATE "C"
This option to change the collation for individual expressions (as opposed to using a collation defined at creation time of the db) was introduced with Postgres 9.1.
More about collation in the manual here.