Postgresql: Check if Schema Exists?
SqlPostgresqlSql Problem Overview
I need to create, manage and drop schemas on the fly. If I go to create a schema that already exists, I want to (conditionally, via external means) drop and recreate it as specified. How can I check for the existence of said schema on my Postgres 9 server?
Currently, I'm doing this:
select exists (select * from pg_catalog.pg_namespace where nspname = 'schemaname');
but I feel like there's probably another way... is this the "proper" way to query Postgres for the existence of a particular schema?
Sql Solutions
Solution 1 - Sql
The following query will tell you whether a schema exists.
SELECT schema_name FROM information_schema.schemata WHERE schema_name = 'name';
Solution 2 - Sql
If you are a total purist or you want to gain some milisecs. I recommend you to make use of postgres native system catalog. One can avoid then nested loop which is caused by calling pg_catalog anyway...
SELECT EXISTS(SELECT 1 FROM information_schema.schemata
WHERE schema_name = 'name');
If you querying pg_namespace directly:
SELECT EXISTS(SELECT 1 FROM pg_namespace WHERE nspname = 'name');
Planer's work is much simpler:
So your own solution was the best.
Solution 3 - Sql
Somewhat related and perhaps of interest to others looking for conditional schema creation. I found myself using code like this in some of my creation scripts:
DO $$
BEGIN
IF NOT EXISTS(
SELECT schema_name
FROM information_schema.schemata
WHERE schema_name = 'pgcrypto'
)
THEN
EXECUTE 'CREATE SCHEMA pgcrypto';
END IF;
END
$$;
Solution 4 - Sql
This can be one of the approaches. Drop the schema first and then create it.
IF EXISTS:
Do not throw an error if the schema does not exist. A notice is issued in this case.
So,
DROP SCHEMA IF EXISTS schema_Name
Create SCHEMA schema_Name
Solution 5 - Sql
If you want to create a schema if it doesn't exist you can just execute:
CREATE SCHEMA IF NOT EXISTS foo
Source: https://www.postgresql.org/docs/current/sql-createschema.html
Solution 6 - Sql
From http://www.postgresql.org/docs/9.1/static/infoschema-schemata.html (emphasis my own):
> The view schemata contains all schemas in the current database that are owned by a currently enabled role.
So your original solution/query is more reliable than Peter's, albeit non-standard.
Solution 7 - Sql
Use
SELECT EXISTS (SELECT 1 FROM pg_catalog.pg_namespace WHERE nspowner <> 1 AND nspname = 'schemaname');
If you check https://www.postgresql.org/docs/current/static/infoschema-schemata.html, you see
> The view schemata contains all schemas in the current database that the current user has access to (by way of being the owner or having some privilege).
This means the query in accepted answer using information_schema.schemata doesn't show schemas that the current user isn't the owner of or doesn't have the USAGE privilege on.
SELECT 1
FROM pg_catalog.pg_namespace
WHERE nspowner <> 1 -- ignore tables made by postgres itself
AND nspname = 'schemaname';
is more complete and will show all existing schemas that postgres didn't make itself regardless of whether or not you have access to the schema.
Solution 8 - Sql
This one worked for me (Postgres 9.3):
Select exists (SELECT 1 FROM information_schema.schemata where catalog_name = 'My_BD_with_UpperCase_characters_in_its_Name')
Solution 9 - Sql
This is valid for the PostgreSQL that will check if the schema if exist and if not then will create it:
CREATE SCHEMA IF NOT EXISTS tenant;
Solution 10 - Sql
NONE of those will work if you have objects (tables,sprocs,views) within a particular schema - IT WILL FAIL during DROP...
CREATE & MANAGE is the easy part.. It's the drop that will get you.. Anyways, I couldn't find a suitable answer, so I posted here for others..