The PostgreSQL system catalog (pg_catalog) is a schema whose tables contain information about the metadata of objects such as repos, tables, views, and columns in bit.io. The pg_catalog schema is created and managed entirely by the Postgres backend and is read-only. By default, pg_catalog is included in the search path, so it isn't necessary to access its tables with schema-qualified names.

`pg_attribute`

The pg_attribute table in the pg_catalog contains information about table columns. Some columns of interest in the table include:

Column Name	Description
`attrelid`	oid of the column's table in `pg_class`
`attname`	name of the column
`atttypid`	data type of the column
`atttisdropped`	indicates whether the column has been dropped from its table and is no longer valid

You can find a full list of columns in the pg_attribute table in the official PostgreSQL documentation.

Example usage

SELECT attname, atttypid FROM pg_attribute WHERE attnotnull = true;

Selects the column name and data type of all columns whose NOT NULL constraint is set to true

`pg_class`

The pg_class table in the pg_catalog schema contains information about tables and views in bit.io. Some of columns of interest in the table include:

Column Name	Description
`relname`	name of the table or view
`relnamespace`	oid of the relation's parent schema in `pg_namespace`
`relkind`	`'r'` = ordinary table, `'v'` = view

You can find a full list of columns in the pg_class table in the official PostgreSQL documentation.

Example usage

SELECT relname  FROM pg_class WHERE relkind = 'v';

Selects the name of all relations with type VIEW.

`pg_namespace`

The pg_namespace table in the pg_catalog schema contains information about repositories in bit.io. Columns in the table include:

Column Name	Description
`oid`	row identifier
`nspname`	name of the repository

You can find a full list of columns in the pg_namespace table in the official PostgreSQL documentation.

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In PostgreSQL, pg_namespace contains information about schemas, which map to repositories in bit.io.

Example usage

SELECT nspname FROM pg_namespace;

Selects the names of all repositories in bit.io.

`pg_roles`

The pg_roles table in the pg_catalog schema contains information about the database roles in bit.io. Some columns of interest include:

`rolname`	Role name
`rolcreaterole`	Role can create more roles
`rolcanlogin`	Role can login

You can find a full list of columns in the pg_roles table in the official PostgreSQL documentation.

Example usage:

SELECT * FROM pg_roles where rolcanlogin = true

Selects all roles that can login.

`pg_tables`

The pg_tables table in the pg_catalog schema contains information about tables in bit.io. Some columns of interest in the table include:

Column Name	Description
`schemaname`	name of the repository the table is in
`tablename`	name of the table

You can find a full list of columns in the pg_tables table in the official PostgreSQL documentation.

Example usage:

SELECT tablename FROM pg_tables WHERE schemaname = 'MyRepo'

Selects the names of all tables in the repository MyRepo.

`pg_views`

The pg_views table in the pg_catalog schema contains information about views in bit.io. Some columns of interest in the table include:

Column Name	Description
`schemaname`	name of the repository the view is in
`viewname`	name of the view
`definition`	definition of the view (in the form of a `SELECT` query)

You can find a full list of columns in the pg_views table in the official PostgreSQL documentation.

Example usage:

SELECT definition FROM pg_views WHERE schemaname = 'MyRepo' AND viewname = 'MyView'

Selects the definition of a view within the repository MyRepo with name MyView.