Understanding PostgreSQL Queries for Table Names

• PostgreSQL is a powerful open-source relational database management system (RDBMS) used for storing and managing data.
• It uses SQL (Structured Query Language) for interacting with the database.

Listing Table Names:

• You might want to see a list of all tables in your database for various reasons, such as understanding the data schema, managing backups, or migrating data.
• A PostgreSQL query is a specific SQL statement used to retrieve or manipulate data within the database.

information_schema:

• PostgreSQL provides a special schema called information_schema.
• This schema contains pre-defined tables and views that offer information about the database itself, including details about tables.
• It allows you to query these pre-defined structures to get information without needing to directly access internal system tables.

The Query:

Here's a common PostgreSQL query to list all table names:

SELECT table_name
FROM information_schema.tables;

• SELECT table_name: This part specifies that we want to retrieve the table_name column.
• FROM information_schema.tables: This part tells the query to get data from the tables table within the information_schema schema. This tables table holds information about all the tables in the current database.

Filtering by Schema (Optional):

By default, the above query lists tables from all schemas in the database. If you only want tables from specific schemas, like postgresql or postgresql-9.2 (which likely don't exist as schema names), you can add a WHERE clause:

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

postgresql and postgresql-9.2:

• These terms likely refer to the context in which you encountered this query.
• They probably don't represent actual schema names in a typical PostgreSQL database.
• The information_schema typically holds information about user-created schemas, not internal PostgreSQL schemas.

SELECT table_name
FROM information_schema.tables;

This query retrieves the table_name for all tables in all schemas within the current database.

Listing Tables from a Specific Schema (if it exists):

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

This query retrieves the table_name for all tables specifically from the public schema (assuming it exists in your database). Replace 'public' with your desired schema name if it's different.

Using psql (PostgreSQL command-line tool):

Here's how you can achieve the same results using the psql command-line tool:

1. Connect to your PostgreSQL database using psql:

psql -h hostname -d database_name -U username

Replace hostname, database_name, and username with your specific connection details.

1. List all tables:

\dt;

This command will display all tables in all schemas for the current database.

\dt public;  -- Replace 'public' with your schema name

This command will display all tables from the specified schema.

This system catalog table holds information about all database objects, including tables. However, it's generally recommended to use information_schema.tables for better portability and adherence to SQL standards.

SELECT relname AS table_name
FROM pg_catalog.pg_class
WHERE relkind = 'r'  -- Filter for tables (relation kind 'r')
  AND relname !~ '^pg_|sql_' -- Exclude internal tables; adjust pattern as needed
;

Using pg_list_tables():

This built-in function returns a recordset containing information about tables in the current schema. It's less common than the information_schema approach but can be useful in specific situations.

SELECT table_name
FROM pg_list_tables();

Using psql commands:

The psql command-line tool offers shortcuts for viewing tables:

• \dt: Lists all tables and views in the current database.
• \dt+: Provides more detailed information about tables and views.
• \dT <schema_name>: Lists tables specifically from a particular schema.

Choosing the Right Method:

• For general usage and portability, information_schema.tables is the recommended approach.
• If you need more control over filtering internal system tables, pg_catalog.pg_class might be suitable (use with caution).
• pg_list_tables() is less common but an option for specific scenarios.
• psql commands offer a convenient way to interact with tables from the command line.