COUNT, SUM, AVG, MIN, MAX in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the COUNT() function do in SQL?

COUNT() returns the number of rows that match a specified condition or all rows if no condition is given.

beginner

How does the SUM() function work in SQL?

SUM() adds up all the values in a numeric column and returns the total sum.

beginner

What is the purpose of the AVG() function?

AVG() calculates the average (mean) value of a numeric column by adding all values and dividing by the count.

beginner

Explain what MIN() and MAX() functions do.

MIN() returns the smallest value in a column, and MAX() returns the largest value in a column.

intermediate

Can aggregate functions like COUNT(), SUM(), AVG(), MIN(), MAX() be used without GROUP BY?

Yes, they can be used without GROUP BY to calculate values over the entire table or filtered rows.

Which SQL function counts the number of rows in a table?

A AVG()

B SUM()

C COUNT()

D MAX()

COUNT() counts rows, while SUM(), AVG(), and MAX() perform calculations on column values.

What does SUM(salary) return in a table of employees?

A The total sum of all salaries

B The average salary

C The highest salary

D The total number of employees

SUM() adds all salary values to give the total sum.

Which function would you use to find the smallest value in a column?

A MAX()

B AVG()

C COUNT()

D MIN()

MIN() returns the smallest value in a column.

If you want the average price of products, which function is correct?

A AVG(price)

B SUM(price)

C COUNT(price)

D MAX(price)

AVG() calculates the average value of the price column.

Can you use aggregate functions without GROUP BY to get a single summary value?

A No, GROUP BY is always required

B Yes, it returns a summary for the whole table

C Only COUNT() can be used without GROUP BY

D Only SUM() and AVG() can be used without GROUP BY

Aggregate functions can be used without GROUP BY to summarize the entire table.

Describe how COUNT(), SUM(), AVG(), MIN(), and MAX() functions work in SQL.

Think about what each function returns when applied to a column.

Explain when you would use aggregate functions with and without GROUP BY.

Consider how grouping changes the output of aggregate functions.