What is the difference between COUNT(*) and COUNT(column_name)?

There is no difference; they yield the same result.

COUNT(*) counts all rows containing data, while COUNT(column_name) counts only unique values.

COUNT(*) counts all rows (including NULLs), while COUNT(column_name) counts only rows where that specific column is NOT NULL.

COUNT(*) is used for integers, while COUNT(column_name) is used for strings.

Which function would you use to combine the first_name and last_name columns into a single column named full_name?

CONCAT(first_name, ' ', last_name)

medium #sql #sql-functions

QUESTION 01 OF 05

SQL functions

These cover common aggregate, string, and handling functions.

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Which function returns the first non-null value in a list of arguments?

About this Quiz

This interactive assessment is designed to test your understanding of SQL functions. Whether you are a beginner looking to grasp the basics or an experienced professional aiming to refine your skills, quizzes are an excellent way to validate your knowledge and identify areas for improvement.

Instructions

Read each question carefully before answering.
Some questions may have multiple correct answers.
There is no time limit, so take your time to think.
You will receive immediate feedback after submission.

Learning Outcomes

Self-assess your current skill level.
Reinforce key concepts through active recall.
Identify knowledge gaps to focus your study.
Gain confidence in your technical expertise.
Reinforce memory and recall.

Topic Overview

These cover common aggregate, string, and handling functions.