Generating a UUID in Postgres for Insert statement?
My question is rather simple. I'm aware of the concept of a UUID and I want to generate one to refer to each 'item' from a 'store' in my DB with. Seems reasonable right?
The problem is the following line returns an error:
honeydb=# insert into items values(
uuid_generate_v4(), 54.321, 31, 'desc 1', 31.94);
ERROR: function uuid_generate_v4() does not exist
LINE 2: uuid_generate_v4(), 54.321, 31, 'desc 1', 31.94);
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
I've read the page at: http://www.postgresql.org/docs/current/static/uuid-ossp.html
I'm running Postgres 8.4 on Ubuntu 10.04 x64.
uuid-ossp is a contrib module, so it isn't loaded into the server by default. You must load it into your database to use it.
For modern PostgreSQL versions (9.1 and newer) that's easy:
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
but for 9.0 and below you must instead run the SQL script to load the extension. See the documentation for contrib modules in 8.4.
For Pg 9.1 and newer instead read the current contrib docs and CREATE EXTENSION . These features do not exist in 9.0 or older versions, like your 8.4.
If you're using a packaged version of PostgreSQL you might need to install a separate package containing the contrib modules and extensions. Search your package manager database for 'postgres' and 'contrib'.
Without extensions (cheat)
SELECT uuid_in(md5(random()::text || now()::text)::cstring);
output>> c2d29867-3d0b-d497-9191-18a9d8ee7830
(works at least in 8.4)
Good point from @Erwin Brandstetter
SELECT uuid_in(md5(random()::text || clock_timestamp()::text)::cstring);
Also, in modern Postgres, you can simply cast:
SELECT md5(random()::text || clock_timestamp()::text)::uuid - no need for more magic
The answer by Craig Ringer is correct. Here's a little more info for Postgres 9.1 and later…
Is Extension Available?
You can only install an extension if it has already been built for your Postgres installation (your cluster in Postgres lingo). For example, I found the uuid-ossp extension included as part of the installer for Mac OS X kindly provided by EnterpriseDB.com. Any of a few dozen extensions may be available.
To see if the uuid-ossp extension is available in your Postgres cluster, run this SQL to query the pg_available_extensions system catalog:
SELECT * FROM pg_available_extensions;
Install Extension
To install that UUID-related extension, use the CREATE EXTENSION command as seen in this this SQL:
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
Beware: I found the QUOTATION MARK characters around extension name to be required, despite documentation to the contrary.
The SQL standards committee or Postgres team chose an odd name for that command. To my mind, they should have chosen something like "INSTALL EXTENSION" or "USE EXTENSION".
Verify Installation
You can verify the extension was successfully installed in the desired database by running this SQL to query the pg_extension system catalog:
SELECT * FROM pg_extension;
UUID as default value
For more info, see the Question: Default value for UUID column in Postgres
The Old Way
The information above uses the new Extensions feature added to Postgres 9.1. In previous versions, we had to find and run a script in a .sql file. The Extensions feature was added to make installation easier, trading a bit more work for the creator of an extension for less work on the part of the user/consumer of the extension. See my blog post for more discussion.
Types of UUIDs
By the way, the code in the Question calls the function uuid_generate_v4() . This generates a type known as Version 4 where nearly all of the 128 bits are randomly generated. While this is fine for limited use on smaller set of rows, if you want to virtually eliminate any possibility of collision, use another "version" of UUID.
For example, the original Version 1 combines the MAC address of the host computer with the current date-time and an arbitrary number, the chance of collisions is practically nil.
For more discussion, see my Answer on related Question.
链接地址: http://www.djcxy.com/p/91430.html上一篇: 独一无二的标识，无需在Ajax中提交表单