psql command-line tool basics in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this psql command?

You run the command \dt inside the psql tool connected to a database with three tables: users, orders, and products. What will be displayed?

PostgreSQL

\dt

A A list of all databases available on the server

B An error saying '\dt' is not recognized

C A list showing the three tables: users, orders, products with their schema and type

D The content of the users table

💡 Hint

The \dt command lists tables in the current database.

The \dt command in psql shows all tables in the current database schema. It does not show databases or table contents.

📝 Syntax

intermediate

Which psql command correctly connects to a database named 'shopdb'?

You want to connect to the database named 'shopdb' using psql. Which command will do this?

A psql -d shopdb

B psql connect shopdb

C psql --database=shopdb

D psql shopdb

💡 Hint

psql accepts the database name as the first argument or with -d option.

The simplest ways to connect to a database are 'psql shopdb' or 'psql -d shopdb'. Option C is invalid syntax; option B is invalid.

🔧 Debug

advanced

Why does this psql command fail?

You run the command SELECT * FROM users\; inside psql and get a syntax error. Why?

PostgreSQL

SELECT * FROM users\;

A The semicolon is missing at the end of the statement

B psql commands cannot be run inside SQL statements

C The table 'users' does not exist

D The backslash before the semicolon is invalid syntax in SQL

💡 Hint

Backslash is used for psql commands, not inside SQL statements.

The backslash before the semicolon is not valid SQL syntax. The semicolon alone ends the statement. Backslash commands are separate from SQL.

🧠 Conceptual

advanced

What does the psql command \x do?

You type \x in the psql prompt. What is the effect?

A It toggles expanded output mode, showing query results vertically

B It exits the psql tool

C It shows the current database connection info

D It lists all indexes in the current database

💡 Hint

Expanded mode changes how query results are displayed.

The \x command toggles expanded output mode, which shows each column on its own line for easier reading of wide tables.

❓ optimization

expert

Which psql command efficiently imports a large SQL file named 'backup.sql' into the current database?

You want to load a large SQL dump file 'backup.sql' into your current database using psql. Which command is best?

A \i backup.sql

B \load backup.sql

C psql -f backup.sql

D \copy backup.sql

💡 Hint

The \i command runs SQL commands from a file inside psql.

The \i command inside psql reads and executes SQL commands from a file. Option A runs psql from shell, not inside psql. \copy is for data import/export, not SQL scripts. \load is for loading shared libraries.