How to Loop Over A List Of Schemas In PostgreSQL?

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To loop over a list of schemas in PostgreSQL, you can use PL/pgSQL (a procedural language available in PostgreSQL) to write a script. Here's an example of how you can achieve this:

  1. Create a function in PL/pgSQL by using the CREATE OR REPLACE FUNCTION statement. The function will loop over each schema in the list and execute some commands.
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CREATE OR REPLACE FUNCTION loop_over_schemas()
  RETURNS VOID
  LANGUAGE plpgsql
AS $$
DECLARE
  schema_name TEXT;
BEGIN
  -- Create a cursor to fetch all schema names
  FOR schema_name IN SELECT schema_name FROM information_schema.schemata LOOP
    -- Execute commands for each schema
    -- Replace 'your_command' with the desired command or query
    EXECUTE 'your_command' USING schema_name;
  END LOOP;
END;
$$;


  1. Replace 'your_command' with the command or query you want to execute for each schema. You can access the current schema name using the schema_name variable.
  2. Call the function using the SELECT statement:
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SELECT loop_over_schemas();


This will execute the loop and run the specified command for each schema in the list.


Note: Ensure that you have the necessary privileges to access and execute the commands for the schemas in the list.

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How to retrieve schema owners in PostgreSQL while looping over schemas?

To retrieve schema owners in PostgreSQL while looping over schemas, you can use the following steps:

  1. Connect to your PostgreSQL database using a database client or command-line tool.
  2. Use the following query to retrieve a list of all schemas in the database: SELECT schema_name FROM information_schema.schemata WHERE schema_owner != 'postgres'; This query retrieves all schemas except for the default postgres schema.
  3. Loop over the result set from the above query and execute the following query to retrieve the owner for each schema: SELECT nspname AS schema_name, rolname AS owner_name FROM pg_namespace JOIN pg_roles ON nspowner = pg_roles.oid WHERE nspname = ''; Replace with the actual schema name obtained from the previous query. This query joins the pg_namespace and pg_roles system catalogs to get the schema name and owner name based on the schema's owner ID.
  4. Process the result set from the owner query as per your requirements. For example, you could print the schema name and owner name: DO $$ DECLARE schema_name text; owner_name text; BEGIN FOR schema_name IN (SELECT schema_name FROM information_schema.schemata WHERE schema_owner != 'postgres') LOOP EXECUTE format('SELECT nspname, rolname FROM pg_namespace JOIN pg_roles ON nspowner = pg_roles.oid WHERE nspname = ''%s''', schema_name) INTO schema_name, owner_name; RAISE NOTICE 'Schema: %, Owner: %', schema_name, owner_name; END LOOP; END $$ LANGUAGE plpgsql; This is an example of a PL/pgSQL block that loops over all non-postgres schemas and retrieves and prints the schema name and owner name.


Note: This solution assumes that you have sufficient privileges to access the necessary system catalogs and retrieve the schema owners' information.


What is the importance of looping over schemas in PostgreSQL?

Looping over schemas in PostgreSQL allows for various important tasks, including:

  1. Schema management: By iterating over schemas, you can perform schema creation, modification, or deletion processes. This is particularly useful when working with multiple schemas, as it simplifies the management of schemas in bulk.
  2. Data organization and partitioning: Looping over schemas enables you to partition data into separate logical units. This can help improve performance, maintainability, and scalability of the database.
  3. Security and access control: Schemas allow you to define different access privileges and restrictions for different user groups or roles. Looping over schemas can simplify the process of granting or revoking access rights for multiple schemas simultaneously.
  4. Cross-schema operations: Looping over schemas allows you to perform operations that span across multiple schemas, such as querying or manipulating data across different schemas within a single transaction.
  5. Schema versioning and migration: When managing application schemas, looping over schemas can assist in versioning and migrating database schemas. This helps ensure that applications remain compatible with the underlying database structure during upgrades or changes.


Overall, looping over schemas in PostgreSQL provides flexibility, scalability, and security to easily manage and organize data within a database.


How to count the number of schemas in PostgreSQL?

To count the number of schemas in PostgreSQL, you can use the following SQL query:

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SELECT count(*) AS total_schemas
FROM information_schema.schemata;


This query retrieves the count of all schemas from the information_schema.schemata view. The result will be a single row containing the total number of schemas present in your PostgreSQL database.

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