Creating databases and tables in Hadoop - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Hive query?

Consider the following Hive query to create a database and then list all databases. What will be the output of the SHOW DATABASES; command?

Hadoop

CREATE DATABASE IF NOT EXISTS sales_db;
SHOW DATABASES;

A ["default"]

B ["default", "sales_db"]

C SyntaxError

D []

💡 Hint

Think about what databases exist by default and what happens when you create a new one.

The CREATE DATABASE IF NOT EXISTS sales_db; command creates a new database named 'sales_db' if it does not already exist. The SHOW DATABASES; command lists all databases including the default one and the newly created 'sales_db'.

❓ data_output

intermediate

How many tables are in the database after these commands?

Given the following Hive commands, how many tables will be listed in sales_db?

Hadoop

CREATE DATABASE IF NOT EXISTS sales_db;
USE sales_db;
CREATE TABLE IF NOT EXISTS customers (id INT, name STRING);
CREATE TABLE IF NOT EXISTS orders (order_id INT, customer_id INT);
SHOW TABLES;

A SyntaxError

B 0

C 1

D 2

💡 Hint

Count how many tables you created in the database.

Two tables, 'customers' and 'orders', are created in the 'sales_db' database. The SHOW TABLES; command lists both tables, so the count is 2.

🔧 Debug

advanced

Identify the error in this Hive table creation command

What error will this Hive query produce?

Hadoop

CREATE TABLE employees (id INT, name STRING, salary);

A SyntaxError: Missing data type for column 'salary'

B No error, table created successfully

C TypeError: Invalid column name

D RuntimeError: Table already exists

💡 Hint

Check if all columns have data types specified.

The column 'salary' does not have a data type specified, which causes a syntax error in Hive table creation.

🧠 Conceptual

advanced

What is the difference between EXTERNAL and MANAGED tables in Hive?

Choose the correct statement about EXTERNAL and MANAGED tables in Hive.

A Dropping a MANAGED table deletes both metadata and data; dropping an EXTERNAL table deletes only metadata.

B Dropping an EXTERNAL table deletes both metadata and data; dropping a MANAGED table deletes only metadata.

C Both EXTERNAL and MANAGED tables delete data when dropped.

D Neither EXTERNAL nor MANAGED tables delete data when dropped.

💡 Hint

Think about who manages the data files for each table type.

MANAGED tables store data in Hive's warehouse directory and dropping them deletes data and metadata. EXTERNAL tables point to data stored outside Hive's control, so dropping them deletes only metadata, leaving data intact.

🚀 Application

expert

Which command creates a partitioned table in Hive?

You want to create a table named sales partitioned by year and month. Which Hive command correctly creates this partitioned table?

A CREATE TABLE sales PARTITIONED BY (year INT, month INT) (id INT, amount FLOAT);

B CREATE TABLE sales (id INT, amount FLOAT, year INT, month INT) PARTITIONED BY ();

C CREATE TABLE sales (id INT, amount FLOAT) PARTITIONED BY (year INT, month INT);

D CREATE TABLE sales (id INT, amount FLOAT) PARTITION (year INT, month INT);

💡 Hint

Remember the syntax for partitioned tables in Hive: columns go first, then PARTITIONED BY clause.

The correct syntax places the regular columns first, then uses PARTITIONED BY to specify partition columns separately.

Practice

1. What is the main purpose of creating a database in Hadoop?

easy

A. To run queries faster

B. To store data in rows and columns

C. To organize data into separate groups

D. To delete old data automatically

Solution

1. Step 1: Understand the role of a database

   A database is used to organize data logically into separate groups or collections.

2. Step 2: Differentiate database from tables

   Tables store data in rows and columns inside a database, but the database itself is for grouping.

3. Final Answer:

   To organize data into separate groups -> Option C

4. Quick Check:

   Database = Organize data groups [OK]

Hint: Databases group data; tables hold the data [OK]

Common Mistakes:

• Confusing database with table
• Thinking database stores data directly
• Assuming database speeds up queries automatically

2. Which of the following is the correct syntax to create a database named sales_db in Hive?

easy

A. CREATE DATABASE sales_db;

B. MAKE DATABASE sales_db;

C. CREATE DB sales_db;

D. NEW DATABASE sales_db;

Solution

1. Step 1: Recall Hive syntax for database creation

   The correct command to create a database in Hive is CREATE DATABASE database_name;.

2. Step 2: Check each option

   Only CREATE DATABASE sales_db; matches the correct syntax exactly.

3. Final Answer:

   CREATE DATABASE sales_db; -> Option A

4. Quick Check:

   CREATE DATABASE = correct syntax [OK]

Hint: Use CREATE DATABASE, not MAKE or NEW [OK]

Common Mistakes:

• Using MAKE or NEW instead of CREATE
• Abbreviating DATABASE as DB
• Missing semicolon at end

3. What will be the result of running this Hive query?

CREATE TABLE employees (id INT, name STRING, salary FLOAT);

medium

A. Creates a table named employees with three columns

B. Throws a syntax error due to missing database name

C. Creates a database named employees

D. Creates a table with no columns

Solution

1. Step 1: Analyze the CREATE TABLE statement

   The query uses correct syntax to create a table named employees with columns id, name, and salary.

2. Step 2: Check for errors or missing parts

   Database name is optional if default database is used; no syntax error here.

3. Final Answer:

   Creates a table named employees with three columns -> Option A

4. Quick Check:

   CREATE TABLE with columns = creates table [OK]

Hint: CREATE TABLE defines columns inside parentheses [OK]

Common Mistakes:

• Thinking database name is mandatory
• Confusing table and database creation
• Assuming syntax error without checking carefully

4. Identify the error in this Hive query:

CREATE TABLE users id INT, name STRING;

medium

A. Table name is invalid

B. Missing parentheses around column definitions

C. Data types are incorrect

D. CREATE TABLE keyword is misspelled

Solution

1. Step 1: Review the syntax for CREATE TABLE

   Column definitions must be enclosed in parentheses after the table name.

2. Step 2: Check the given query

   The query misses parentheses around id INT, name STRING, causing syntax error.

3. Final Answer:

   Missing parentheses around column definitions -> Option B

4. Quick Check:

   Columns need parentheses [OK]

Hint: Always use parentheses for columns in CREATE TABLE [OK]

Common Mistakes:

• Forgetting parentheses
• Assuming table name is wrong
• Thinking data types are invalid

5. You want to create a database company_db and inside it a table departments with columns dept_id INT and dept_name STRING. Which sequence of commands is correct?

hard

A. CREATE TABLE company_db.departments (dept_id INT, dept_name STRING);

B. CREATE DATABASE company_db; CREATE TABLE departments dept_id INT, dept_name STRING;

C. USE company_db; CREATE DATABASE company_db; CREATE TABLE departments (dept_id INT, dept_name STRING);

D. CREATE DATABASE company_db; USE company_db; CREATE TABLE departments (dept_id INT, dept_name STRING);

Solution

1. Step 1: Create the database first

   Use CREATE DATABASE company_db; to make the database.

2. Step 2: Switch to the new database

   Use USE company_db; to set the context for table creation.

3. Step 3: Create the table with correct syntax

   Use CREATE TABLE departments (dept_id INT, dept_name STRING); inside the database.

4. Final Answer:

   CREATE DATABASE company_db; USE company_db; CREATE TABLE departments (dept_id INT, dept_name STRING); -> Option D

5. Quick Check:

   Create DB, switch DB, then create table [OK]

Hint: Create DB, then USE it before creating tables [OK]

Common Mistakes:

• Trying to create table before database
• Wrong order of USE and CREATE DATABASE
• Missing parentheses in CREATE TABLE