How to List Tables in Different Schemas (PostgreSQL)

• PostgreSQL: A powerful open-source object-relational database management system (DBMS).
• Schema: A logical grouping of database objects (tables, views, sequences, etc.) that helps organize and manage them.
• psql: The command-line interface (CLI) tool for interacting with PostgreSQL servers.

Steps:

1. Connect to your PostgreSQL server:

2. List tables using pg_catalog.pg_tables system catalog view:

Explanation:

• information_schema.tables: This built-in view provides information about all tables in the current database, including their schema names.
• table_name: This column holds the name of each table.
• WHERE table_schema NOT IN ('pg_catalog', 'information_schema'): This condition filters out tables belonging to the system schemas (pg_catalog contains system tables and information_schema contains metadata tables).

Output:

The query will display a list of table names, one per row, belonging to user-defined schemas in the database.

Additional Notes:

• You can modify the query to list specific columns by adding them to the SELECT clause (e.g., SELECT table_name, table_schema).
• To list tables from a particular schema, replace NOT IN ('pg_catalog', 'information_schema') with = 'your_schema_name'.

SELECT table_name
FROM information_schema.tables
WHERE table_schema NOT IN ('pg_catalog', 'information_schema');

Listing tables from a specific schema (replace your_schema_name with the actual schema name):

SELECT table_name
FROM information_schema.tables
WHERE table_schema = 'your_schema_name';

• This code modifies the previous query to include a specific schema name (your_schema_name) in the WHERE clause.
• This will only list tables that belong to the specified schema.

Remember:

• Replace <username> and <database_name> in the connection command with your actual credentials.
• Execute these code snippets within the psql client after connecting to your PostgreSQL server.

This method leverages the built-in \dt command in the psql client. It offers flexibility with wildcards for schema and table names.

psql -U <username> <database_name>

# List all tables from all schemas:
\dt *.*

# List all tables from a specific schema (replace 'public' with your schema name):
\dt public.*

# Use regular expressions for more complex filtering (refer to psql documentation for details):
\dt (schema1|schema2).(table_pattern)  # List tables matching pattern from schema1 or schema2

Using pg_tables system catalog view (psql):

This method employs the pg_tables system catalog view similar to the previous approach but provides more control over the output columns.

SELECT table_name, table_schema, table_type  -- Add or remove columns as needed
FROM pg_catalog.pg_tables
WHERE table_schema NOT IN ('pg_catalog', 'information_schema');

Information schema views (psql):

PostgreSQL offers several information schema views for introspection. While not as widely used for listing tables, they provide a different perspective:

• information_schema.schemata: Lists all schemas in the database.
• information_schema.tables: Lists all tables in the database (including system schemas).

You can combine these views with filtering to achieve similar results. However, the information_schema.tables approach requires filtering system schemas as shown previously.

Choosing the Right Method:

• If you prefer a simple command-line approach with wildcards, \dt is a good choice.
• If you need more granular control over the output columns or prefer a pure SQL approach, the information_schema.tables method with filtering is ideal.
• Information schema views might be useful for exploring schema information beyond just tables.