Database creation and selection in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this query?

Given the following SQL commands:

CREATE DATABASE IF NOT EXISTS shop;
USE shop;
SHOW DATABASES LIKE 'shop';

What will be the output of the last command?

MySQL

CREATE DATABASE IF NOT EXISTS shop;
USE shop;
SHOW DATABASES LIKE 'shop';

A An empty result set

B A single row with the database name 'shop'

C A syntax error due to missing semicolon

D All databases including 'shop' and others

💡 Hint

SHOW DATABASES LIKE 'pattern' returns databases matching the pattern.

The command SHOW DATABASES LIKE 'shop' returns only databases named exactly 'shop'. Since it was created, it appears as one row.

📝 Syntax

intermediate

Which option correctly creates a database named 'library'?

Choose the correct SQL statement to create a database named 'library' only if it does not already exist.

A CREATE DATABASE IF NOT EXISTS library;

B CREATE DB IF NOT EXISTS library;

C CREATE DATABASE IF EXIST library;

D CREATE DATABASE library;

💡 Hint

The correct syntax uses IF NOT EXISTS to avoid errors if the database exists.

Option A uses the correct syntax to create the database only if it does not exist. Options B and C are invalid syntax, and A will error if the database exists.

❓ query_result

advanced

What is the result of this sequence of commands?

Consider these commands:

CREATE DATABASE testdb;
USE testdb;
CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(50));
SHOW TABLES;

What will SHOW TABLES return?

MySQL

CREATE DATABASE testdb;
USE testdb;
CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(50));
SHOW TABLES;

A A syntax error due to missing semicolon

B An empty list because no tables exist

C A list containing one table named 'users'

D A list of all tables in all databases

💡 Hint

SHOW TABLES shows tables in the current database.

After creating the 'users' table in 'testdb' and selecting it with USE, SHOW TABLES returns the list of tables in 'testdb', which includes 'users'.

🔧 Debug

advanced

Why does this command fail?

Given the command:

USE shop_db;

It produces an error. What is the most likely cause?

MySQL

USE shop_db;

A Incorrect database name syntax

B Missing semicolon at the end of the statement

C USE command is not supported in MySQL

D Database 'shop_db' does not exist

💡 Hint

SQL statements must end with a semicolon.

If the command includes a semicolon, the most likely cause of error is that the database 'shop_db' does not exist. USE is valid and database names can have underscores.

🧠 Conceptual

expert

Which statement about database selection is true?

Select the correct statement about the USE command in MySQL.

A USE changes the current database for the session until changed again

B USE creates a new database if it does not exist

C USE lists all available databases

D USE deletes the current database

💡 Hint

Think about what USE does to your working environment.

The USE command sets the current database for the session. It does not create, list, or delete databases.

Practice

1. What does the CREATE DATABASE command do in MySQL?

easy

A. It selects a database to use.

B. It deletes an existing database.

C. It creates a new database to store data.

D. It shows all databases available.

Solution

1. Step 1: Understand the purpose of CREATE DATABASE

   This command is used to make a new database where you can store tables and data.

2. Step 2: Differentiate from other commands

   Deleting databases uses DROP DATABASE, selecting uses USE, and showing uses SHOW DATABASES.

3. Final Answer:

   It creates a new database to store data. -> Option C

4. Quick Check:

   CREATE DATABASE = create new database [OK]

Hint: Remember: CREATE makes new, USE picks existing [OK]

Common Mistakes:

• Confusing CREATE with USE command
• Thinking CREATE deletes databases
• Mixing CREATE with SHOW DATABASES

2. Which of the following is the correct syntax to select a database named shop in MySQL?

easy

A. SELECT DATABASE shop;

B. CHOOSE DATABASE shop;

C. OPEN DATABASE shop;

D. USE shop;

Solution

1. Step 1: Recall the command to select a database

   In MySQL, the command to start using a database is USE database_name;.

2. Step 2: Check each option's syntax

   Only USE shop; is valid syntax. Others are incorrect commands.

3. Final Answer:

   USE shop; -> Option D

4. Quick Check:

   USE selects database [OK]

Hint: Use USE to pick your database [OK]

Common Mistakes:

• Using SELECT instead of USE
• Trying OPEN or CHOOSE commands (not valid)
• Missing semicolon at end

3. What will be the result of the following commands?

CREATE DATABASE testdb;
USE testdb;
SHOW TABLES;

medium

A. Lists all tables in the database 'testdb'.

B. Shows an error because 'testdb' does not exist.

C. Creates a table named 'testdb'.

D. Shows all databases available.

Solution

1. Step 1: Create and select the database

   The command CREATE DATABASE testdb; makes a new database named 'testdb'. Then USE testdb; selects it for use.

2. Step 2: Show tables in the selected database

   SHOW TABLES; lists all tables in the current database. Since 'testdb' is empty, it will show an empty list but no error.

3. Final Answer:

   Lists all tables in the database 'testdb'. -> Option A

4. Quick Check:

   SHOW TABLES lists tables in current DB [OK]

Hint: SHOW TABLES lists tables in current database [OK]

Common Mistakes:

• Thinking SHOW TABLES shows databases
• Assuming error because database is new
• Confusing CREATE DATABASE with CREATE TABLE

4. Identify the error in the following MySQL commands:

CREATE DATABASE mydb
USE mydb;

medium

A. Database name 'mydb' is invalid.

B. Missing semicolon after CREATE DATABASE statement.

C. USE command cannot follow CREATE DATABASE.

D. CREATE DATABASE should be lowercase.

Solution

1. Step 1: Check syntax of each command

   MySQL commands must end with a semicolon. The first line misses a semicolon after CREATE DATABASE mydb.

2. Step 2: Verify other parts

   The database name 'mydb' is valid, USE can follow CREATE DATABASE, and case does not matter for commands.

3. Final Answer:

   Missing semicolon after CREATE DATABASE statement. -> Option B

4. Quick Check:

   Semicolon ends commands [OK]

Hint: Always end SQL commands with semicolon [OK]

Common Mistakes:

• Forgetting semicolon at end of statements
• Thinking database names must be uppercase
• Believing USE cannot follow CREATE DATABASE

5. You want to create two databases named sales and inventory, then select sales to work with. Which sequence of commands is correct?

hard

A. CREATE DATABASE sales; CREATE DATABASE inventory; USE sales;

B. USE sales; CREATE DATABASE sales; CREATE DATABASE inventory;

C. CREATE DATABASE sales, inventory; USE sales;

D. CREATE DATABASE sales; USE inventory; CREATE DATABASE inventory;

Solution

1. Step 1: Create both databases separately

   Each database must be created with its own CREATE DATABASE command ending with a semicolon.

2. Step 2: Select the 'sales' database to use

   After creating, use USE sales; to select the 'sales' database for work.

3. Final Answer:

   CREATE DATABASE sales; CREATE DATABASE inventory; USE sales; -> Option A

4. Quick Check:

   Create each DB then USE the one you want [OK]

Hint: Create each DB separately, then USE the desired one [OK]

Common Mistakes:

• Trying to create multiple databases in one command
• Using USE before creating the database
• Selecting wrong database after creation