The psql meta-command \d tablename is used to describe a relation (table, view, index, etc.). When used with a table name, it displays detailed information about the table's structure, including its columns with their data types, modifiers (like NOT NULL), default values, and any associated indexes, constraints (primary keys, foreign keys, check constraints), and triggers. This command provides a comprehensive overview of the table's definition directly within the psql interactive terminal.

A. \dt tablename: This command lists tables. If a tablename pattern is provided, it filters the list, but it does not describe the detailed structure of a specific table.

C. \describe tablename: \describe is not a valid psql meta-command. This might be confused with the DESCRIBE SQL command used in other database systems like MySQL.

D. \show tablename: The \show meta-command is used to display the current value of a PostgreSQL run-time parameter (e.g., \show serverversion), not to describe a database object.

1. PostgreSQL 16 Documentation: In the section on psql meta-commands, the \d command is explicitly defined for this purpose.

Source: PostgreSQL 16 Documentation, Chapter 2. psql, Section: "Meta-Commands", Subsection: "Informational".

Reference: The documentation states: \d[S+] [ pattern ] "For each relation (table, view, materialized view, index, sequence, or foreign table) ... show all columns, their types, the tablespace ... and any special attributes such as NOT NULL or defaults. Associated indexes, constraints, rules, and triggers are also shown."

2. University of California, Berkeley - Courseware: Course materials for database systems frequently cover psql basics, demonstrating the use of \d for schema inspection.

Source: UC Berkeley, EECS Department, CS 186: Introduction to Database Systems, Project 1: Buffer Manager.

Reference: In the "Getting Started with Postgres" section of the project setup guide, students are instructed to use \d tablename to "get information about a table’s schema."

3. PostgreSQL Tutorial Website (Official): The official tutorial provides practical examples of common commands.

Source: PostgreSQL Tutorial, "PostgreSQL psql Commands" section.

Reference: The tutorial lists \d tablename with the description: "Describe a table such as columns, types, and modifiers of columns." It contrasts this with \dt, which is described as "List all tables in the current database."