Database creation and selection in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the SQL command to create a new database named 'library'?

The command is CREATE DATABASE library;. This creates a new empty database called 'library'.

beginner

How do you select a database named 'library' to use it for your queries?

Use the command USE library;. This tells the system to work with the 'library' database for following commands.

intermediate

What happens if you try to create a database that already exists without using any extra options?

You will get an error saying the database already exists. To avoid this, use CREATE DATABASE IF NOT EXISTS database_name;.

beginner

Why is it important to select a database before running queries?

Selecting a database tells the system where to look for tables and data. Without selecting, queries may fail or run on the wrong database.

beginner

Write the SQL commands to create a database named 'school' and then select it for use.

First, create the database: CREATE DATABASE school;
Then select it: USE school;

Which SQL command creates a new database?

A CREATE DATABASE database_name;

B SELECT DATABASE database_name;

C USE database_name;

D DROP DATABASE database_name;

The CREATE DATABASE command is used to create a new database.

How do you tell MySQL to use a specific database for your queries?

A USE database_name;

B CREATE DATABASE database_name;

C SELECT * FROM database_name;

D DROP DATABASE database_name;

The USE command selects the database for your session.

What will happen if you run CREATE DATABASE test; when 'test' already exists?

A It will overwrite the existing database.

B It will create a new database with a different name.

C It will give an error.

D It will delete the existing database.

Trying to create a database that exists causes an error unless you use IF NOT EXISTS.

Which command prevents an error if the database already exists when creating it?

A DROP DATABASE database_name;

B CREATE DATABASE database_name;

C USE database_name;

D CREATE DATABASE IF NOT EXISTS database_name;

Adding IF NOT EXISTS avoids errors if the database exists.

Why do you need to select a database before running queries?

A To delete the database.

B To tell MySQL which database to work with.

C To create a new database.

D To backup the database.

Selecting a database tells MySQL where to find tables and data for your queries.

Explain how to create a new database and select it for use in MySQL.

Think about the two steps: making the database and then telling MySQL to use it.

What is the purpose of the 'IF NOT EXISTS' clause in database creation?

It helps avoid errors when the database is already there.

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