Database creation and selection in MySQL

Introduction

We create databases to store and organize data. We select a database to tell the system which data we want to work with.

When starting a new project and you need a place to store data.

When you want to organize data into separate groups for different purposes.

When you want to switch between different sets of data in your system.

When you want to prepare your system to add tables and data.

When you want to make sure you are working with the right data before running queries.

Syntax

MySQL

CREATE DATABASE database_name;
USE database_name;

Replace database_name with the name you want for your database.

The USE command tells MySQL to work with the chosen database.

Examples

Creates a database named 'school' and selects it for use.

MySQL

CREATE DATABASE school;
USE school;

Creates a database named 'shop' and switches to it.

MySQL

CREATE DATABASE shop;
USE shop;

Creates 'library' only if it does not exist, then selects it.

MySQL

CREATE DATABASE IF NOT EXISTS library;
USE library;

Sample Program

This creates a database named 'testdb' if it doesn't exist and then selects it for use.

MySQL

CREATE DATABASE IF NOT EXISTS testdb;
USE testdb;

Important Notes

Database names should be simple and meaningful.

You can check existing databases with the command: SHOW DATABASES;

Always select the database before creating tables or inserting data.

Summary

Create a database to store your data.

Use the database to tell MySQL which data to work with.

Use 'CREATE DATABASE' and 'USE' commands for these tasks.

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