Creating databases and tables in Hadoop - Quick Revision & Summary

Recall & Review

beginner

What is a database in Hadoop's Hive?

A database in Hive is a namespace that organizes tables. It helps keep data organized like folders on your computer.

beginner

How do you create a new database in Hive?

Use the command:
CREATE DATABASE database_name;
This makes a new space to store tables.

beginner

What is a table in Hive?

A table is like a spreadsheet with rows and columns where data is stored inside a database.

beginner

How do you create a table in Hive?

Use the command:
CREATE TABLE table_name (column1 TYPE, column2 TYPE, ...);
This sets up a table with columns and their data types.

beginner

What data types can you use when creating tables in Hive?

Common types include INT (numbers), STRING (text), FLOAT (decimal numbers), and BOOLEAN (true/false).

Which command creates a new database in Hive?

A CREATE DATABASE mydb;

B MAKE DATABASE mydb;

C NEW DATABASE mydb;

D CREATE TABLE mydb;

The correct syntax to create a database in Hive is CREATE DATABASE followed by the database name.

What does a table in Hive represent?

A A folder to store files

B A spreadsheet-like structure with rows and columns

C A programming function

D A type of database

A table stores data organized in rows and columns, similar to a spreadsheet.

Which data type is used for text in Hive tables?

A FLOAT

B BOOLEAN

C INT

D STRING

STRING is the data type used for text values in Hive tables.

How do you specify columns when creating a table in Hive?

A List column names only

B List data types only

C List column names with data types

D No need to specify columns

You must specify both column names and their data types when creating a table.

What is the purpose of a database in Hive?

A To organize tables into groups

B To store files

C To run queries

D To create users

Databases group tables together to keep data organized.

Explain how to create a database and a table in Hive, including the syntax and purpose of each.

Think about how folders and files work on your computer.

Describe common data types used when creating tables in Hive and why choosing the right type matters.

Consider how you choose the right container for different items.

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