19. Inclusive and non-inclusive comparison

Let’s examine the query to count signups after 1, Jan 2018:

SELECT COUNT(*)
FROM users
WHERE
  signup_date > '2018-01-01'

We used the greater than > non-inclusive operator. Non-inclusive means that signup dates that are exactly '2018-01-01' will be filtered out and we won’t see them in the query’s output

If we want to keep signups from 1st of January we should use inclusive comparison operator greater or equals than >=:

SELECT COUNT(*)
FROM users
WHERE
  signup_date >= '2018-01-01'

Same with numbers, if we want to calculate users who are younger than 50 we can use less than < operator:

SELECT COUNT(*)
FROM users
WHERE
  age < 50

but this query won’t include users who are exactly 50 years old. If we want to filter for 50-year-olds as well we should use less than or equals operator:

SELECT COUNT(*)
FROM users
WHERE
  age <= 50

Keep an eye for such issues Imagine a company had a sale on the last day of the month. Someone calculates monthly revenue and by mistake doesn’t include the last day of the month – the highest revenue day will be excluded from the analysis.

Before you go to the next lesson go and play with inclusive and non-inclusive comparison operators in the Playground and see how counts will differ.