psql command-line tool basics in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to connect to a PostgreSQL database named 'school' using psql.

PostgreSQL

psql [1] school

Drag options to blanks, or click blank then click option'

A-U

B-h

C-d

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-h' which is for host, not database name.

Using '-U' which is for username, not database name.

The -d option specifies the database name to connect to in psql.

2fill in blank

medium

Complete the command to connect to the database 'library' as user 'admin' using psql.

PostgreSQL

psql -d library [1] admin

Drag options to blanks, or click blank then click option'

A-U

B-h

C-p

D-W

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-W' which prompts for password, not username.

Using '-p' which is for port number.

The -U option specifies the username to connect as in psql.

3fill in blank

hard

Fix the error in the command to connect to host 'localhost' on port 5432 using psql.

PostgreSQL

psql -d mydb [1] localhost -p 5432

Drag options to blanks, or click blank then click option'

A-h

B-U

C-d

D-W

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-U' which is for username, not host.

Using '-d' again which is for database name.

The -h option specifies the host to connect to in psql.

4fill in blank

hard

Fill both blanks to run a SQL file named 'setup.sql' on database 'testdb' using psql.

PostgreSQL

psql [1] testdb [2] setup.sql

Drag options to blanks, or click blank then click option'

A-f

B-d

C-U

D-h

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-U' instead of '-d' for database name.

Using '-h' instead of '-f' for file.

Use -d to specify the database and -f to specify the SQL file to run.

5fill in blank

hard

Fill all three blanks to connect to database 'shop', user 'alice', host 'db.example.com' using psql.

PostgreSQL

psql [1] shop [2] alice [3] db.example.com

Drag options to blanks, or click blank then click option'

A-d

B-U

C-h

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up '-U' and '-h' options.

Using '-p' for host instead of port.

Use -d for database, -U for user, and -h for host in psql.

Practice

1. What is the primary purpose of the psql command-line tool in PostgreSQL?

easy

A. To connect to a PostgreSQL database and run SQL commands interactively

B. To create new PostgreSQL database clusters

C. To backup PostgreSQL databases automatically

D. To monitor server hardware performance

Solution

1. Step 1: Understand the role of psql

   psql is a command-line interface tool designed to connect to PostgreSQL databases and allow users to run SQL commands interactively.

2. Step 2: Differentiate from other tools

   Other options like creating clusters or backups are done by different tools or commands, not psql.

3. Final Answer:

   To connect to a PostgreSQL database and run SQL commands interactively -> Option A

4. Quick Check:

   psql = interactive SQL client [OK]

Hint: Remember: psql = PostgreSQL interactive shell [OK]

Common Mistakes:

• Confusing psql with backup tools
• Thinking psql manages hardware
• Assuming psql creates database clusters

2. Which of the following is the correct way to start psql and connect to a database named mydb as user alice?

easy

A. psql start mydb alice

B. psql --connect mydb alice

C. psql connect mydb user alice

D. psql -d mydb -U alice

Solution

1. Step 1: Recall psql connection syntax

   The correct syntax to connect is psql -d database -U user.

2. Step 2: Match options to syntax

   psql -d mydb -U alice matches this syntax exactly, while others use invalid or unsupported flags.

3. Final Answer:

   psql -d mydb -U alice -> Option D

4. Quick Check:

   psql -d db -U user = connect [OK]

Hint: Use -d for database and -U for user [OK]

Common Mistakes:

• Using unsupported flags like --connect
• Writing commands without dashes
• Mixing command words incorrectly

3. Inside psql, what will be the result of running the command \dt?

medium

A. It lists all tables in the current database

B. It deletes the current table

C. It displays the current database connection info

D. It shows the last query execution plan

Solution

1. Step 1: Understand psql meta-commands

   Commands starting with a backslash (\) are special psql commands. \dt lists tables.

2. Step 2: Identify what \dt does

   \dt shows all tables in the current database schema, not deleting or showing connection info.

3. Final Answer:

   It lists all tables in the current database -> Option A

4. Quick Check:

   \dt = list tables [OK]

Hint: Backslash commands show info; \dt lists tables [OK]

Common Mistakes:

• Thinking \dt deletes tables
• Confusing \dt with connection info commands
• Expecting \dt to show query plans

4. You try to run psql -d mydb -U alice but get an error: psql: FATAL: password authentication failed for user "alice". What is the most likely cause?

medium

A. The database mydb does not exist

B. The psql command is misspelled

C. The password entered for user alice is incorrect or missing

D. The PostgreSQL server is not running

Solution

1. Step 1: Analyze the error message

   The error says "password authentication failed for user alice," indicating a login problem.

2. Step 2: Identify the cause

   This usually means the password is wrong or not provided, not that the database or command is missing.

3. Final Answer:

   The password entered for user alice is incorrect or missing -> Option C

4. Quick Check:

   Password error = authentication failed [OK]

Hint: Password errors mean wrong or missing password [OK]

Common Mistakes:

• Assuming database doesn't exist from this error
• Thinking psql command is wrong
• Ignoring server status

5. You want to list all databases available on your PostgreSQL server using psql. Which command should you run inside the psql prompt?

hard

A. SHOW DATABASES;

B. \l

C. \listdb

D. SELECT * FROM pg_databases;

Solution

1. Step 1: Recall psql meta-commands for listing databases

   The command \l (or \list) lists all databases in psql.

2. Step 2: Evaluate other options

   SHOW DATABASES; is MySQL syntax, \listdb is invalid, and SELECT * FROM pg_databases; is incorrect because the catalog table is pg_database, not pg_databases.

3. Final Answer:

   \l -> Option B

4. Quick Check:

   \l = list databases [OK]

Hint: Use \l inside psql to list databases [OK]

Common Mistakes:

• Using MySQL syntax SHOW DATABASES;
• Typing wrong meta-command \listdb
• Querying wrong system table name