Database query optimization in No-Code - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Indexes in Databases

Which of the following best explains how an index improves database query performance?

A It stores a sorted copy of the data to speed up search operations.

B It duplicates all data in the database to reduce access time.

C It compresses the data to use less storage space.

D It automatically deletes old data to keep the database small.

💡 Hint

Think about how a phone book helps you find a name quickly.

An index works like a sorted list that helps the database find data faster without scanning everything.

🔍 Analysis

intermediate

Choosing the Best Query Filter

You have a table with millions of records. Which filter condition will likely make the query run faster?

A Filtering on a column with unique values and an index.

B Filtering on a column without an index and many nulls.

C Filtering on a column with many repeated values.

D Filtering on a column with long text data.

💡 Hint

Indexes work best on columns with unique or selective values.

Filtering on a unique indexed column reduces the search space quickly, improving speed.

❓ Comparison

advanced

Comparing JOIN Types for Performance

Which JOIN type generally requires the least processing time when joining two large tables?

A LEFT OUTER JOIN without indexes

B FULL OUTER JOIN

C INNER JOIN with indexed join keys

D CROSS JOIN

💡 Hint

Think about how indexes help match rows quickly.

INNER JOIN with indexes on join keys allows the database to quickly find matching rows, reducing processing time.

❓ Reasoning

advanced

Impact of SELECT * on Query Speed

Why can using SELECT * in a query slow down database performance?

A It automatically locks the entire table.

B It causes the database to ignore indexes.

C It deletes unused columns from the table.

D It forces the database to return all columns, increasing data transfer and processing.

💡 Hint

Consider how much data is sent back when all columns are requested.

Using SELECT * returns all columns, which can increase the amount of data processed and sent, slowing the query.

🚀 Application

expert

Optimizing Query with Multiple Conditions

Given a query filtering on two columns, which approach is most likely to optimize performance?

Conditions: WHERE age > 30 AND city = 'New York'

A Create an index only on city column.

B Create a composite index on (city, age).

C Create an index only on age column.

D Create separate indexes on age and city columns.

💡 Hint

Think about how combined indexes help with multiple filters.

A composite index on both columns allows the database to efficiently filter using both conditions together.