Data dictionary

List tables

SELECT * FROM pg_catalog.pg_tables;

List indexes (keep in mind the table names are downcase by default)

SELECT * FROM pg_catalog.pg_indexes WHERE tablename = 'some_table'

List views (aren’t included in a list of tables)

SELECT * FROM pg_catalog.pg_views;

Columns

SELECT *
FROM   information_schema.columns
WHERE  table_schema = 'some_schema'
AND    table_name   = 'some_table';

Constraints

SELECT *
FROM   information_schema.table_constraints
WHERE  table_schema = 'some_schema'
AND    table_name   = 'some_table'